One crisp evening last October, a crew filming a piece for VICE on HBO was walking from the Old City of Sanaa, Yemen's capital, to a hotel on the outskirts of nearby Tahrir Square. The sky was bright with the glow of the moon, but there was little other light; the war raging in Yemen had all but destroyed the city's access to electricity, and fuel for generators was in short supply and jealously guarded.

Over the course of the previous two weeks, we had grown accustomed to the sound of fighter jets from the Saudi-led military coalition circling far above us, their arrival announced by the rat-a-tat of anti-aircraft fire and punctuated by the boom of rockets they'd fire into what the coalition said were vital military targets. We thought we were some distance from any such target until, with no warning, a flash of bright orange light and a deafening roar signaled a missile strike no more than 200 meters away. We ran into the hotel lobby as another detonation rattled its windows. The blasts continued for another half an hour.

Elsewhere in Yemen, we had seen tiny water irrigation ditches under country roads expertly targeted with precision airstrikes, so we knew the weapons the coalition was using could be incredibly accurate. What was the high-value target the missiles were aimed at, we wondered?

The next morning we found out. It was a graveyard**.**

For the past year, Saudi Arabia has bombarded the Arab world's poorest country in the hope of dislodging Houthi rebels it says are allied with Iran. The UN's top aid official said earlier this month that airstrikes and the random shelling of civilian areas in the conflict — which has killed, maimed, and displaced thousands of people — "violates cardinal rules of international humanitarian law." This week, a British parliamentary committee announced that it planned to investigate allegations that weapons sold by UK firms to Saudi Arabia — last year, those sales totaled $4.2 billion — were being used to commit war crimes in Yemen. The announcement came three weeks after a separate parliamentary committee in the UK wrote to the government asking it to suspend arms sales to Saudi Arabia, calling for an independent investigation into the kingdom's conduct during the Yemen war.

Saudi Arabia denies any wrongdoing and points to US and UK involvement in the planning of its airstrikes as proof its practices are above board. Why would Washington and London continue to support the aerial campaign with logistics and intelligence, Saudi Arabia argues, if the Saudi-led coalition is breaking international law?

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In January 2015, an alliance of Zaydi Shia militias from the northern Houthi movement, along with tribal fighters and military units loyal to Ali Abdullah Saleh, Yemen's former president, completed a coup d'etat in Sanaa that had been unfolding since the previous September. The coup sparked a civil war, and since last March the Houthi-Saleh alliance has been battling a wide array of rival militias nominally led by the ousted government of Yemeni President Abd Rabbu Mansour Hadi, and backed by Saudi Arabia. The Saudi government, fearing that the Houthis are a Hezbollah-like proxy for their main regional rival, Iran, has spent billions of dollars for an aerial bombing campaign aimed at dislodging the Houthis and Saleh from Sanaa. The goal, in the kingdom's own coded words, is "restoring Yemen's Arab identity."

Announcing its intervention in March 2015, Saudi Arabia confidently predicted that it would require no more than a couple of months to subdue the Houthis and Saleh with the awesome firepower it had built up in recent decades; US congressional research indicates that that the kingdom has spent more than $100 billion on American arms since 2010. The UK is also a major supplier; without huge (and allegedly corrupt) British arms sales to Saudi Arabia, the British weapons industry would have had trouble staying afloat. Saudi Arabia now has more British fighter jets in its air force than the UK has in its own.

The wreckage of a home hit by a coalition airstrike in Sanaa's Old City, a UNESCO World Heritage site. (Photo by Peter Salisbury/VICE News)

By the time we arrived in Yemen in September 2015 to shoot a documentary on the conflict — "Return to Yemen" which airs tonight on VICE on HBO at 11pm ET — it was clear that it would take a lot more time than predicted to win the war, if it could be won militarily at all. What was less clear was the purpose of some of the Saudi-led airstrikes — and whether or not the coalition was accurately targeting pro-Houthi and Saleh fighters in order to avoid hurting or killing civilians as the Geneva Conventions, the basis of international laws of war, demand.

The village of Wahijah is a cluster of straw huts on Yemen's southwestern coast. On September 28 last year, villagers were preparing for the marriage of a local man named Morsal Mohammed Ali to a woman from a nearby settlement. As is customary in Yemen, men and women had gathered in separate huts about 100 yards apart. Coalition fighter planes could be heard above the village, but locals said jets had been regularly flying overhead since the war started. They paid them no mind.

Then two airstrikes hit the huts within a minute of each other. After speaking to locals, the UN, and human rights groups, we estimated that as many as 60 people had been killed; inflated local reports suggested more than double that number had perished in the attack.

We heard about the strike a few minutes after it happened. The following day we traveled from Sanaa to Wahijah, where villagers told us that they had been able to recover only fragments of the bodies of the dead. Skin and musculature flecked the branches of nearby bushes. At one point, a woman picked up the remnants of a scalp and waved it at us.

"They killed everyone!" she cried. "My children, my sister, and all my family!"

There were no fighters in the village, residents said, nor had any come there in the days before the wedding. There were no military installations nearby. Why, they asked, had this happened? The bride and groom had both survived, but the wedding was called off. Like so many young people, their path to adulthood had been put on hold by a conflict that threatens to leave the country in a state of permanent chaos.

A follow-up investigation suggested that the bombing was not necessarily a clear-cut example of an attack on a group of civilians. Several witnesses said that they had seen earlier airstrikes on what they assumed was a nearby military target — either a radar base that might have contained anti-aircraft weapons, or an arms dump. Houthi militants might have also visited the village in the hours before the strikes, contrary to what we were originally told, either to investigate the inflow of people into the area or to wish the families well before the event.

But legally, that still likely wouldn't justify the strikes. In war, international law provides very specific protections to civilians — "persons who are not members of the armed forces," according to the International Committee of the Red Cross, which has a mandate to protect the victims of armed conflicts under the Geneva Conventions. Simply put, people who aren't taking part in fighting shouldn't be targeted by the people who are.

The bed in which an elderly woman was killed by shrapnel from an apparent coalition air strike in Wahijah village. (Photo by Peter Salisbury/VICE News)

International law acknowledges that civilians might sometimes be killed or injured in the course of an attack on a military target. But it also stipulates "proportionality" — the value of the target must justify the risk of killing or injuring innocent people, and attacks cannot be indiscriminate. International law also prohibits assaults on what are known as "civilian objects" like hospitals and schools.

A mounting body of evidence suggests that both the Saudi-led coalition and the alliance of the Houthis and forces loyal to Saleh may have broken the law. Since the beginning of the war, human rights organizations have documented more than 100 individual coalition airstrikes that could be in violation, accounting for more than 1,000 deaths. [We have complied them into a single document, which you can access here.]

A monthly briefing distributed internally by the UN's Office of the High Commissioner for Human Rights (OHCHR) at the end of February and obtained by VICE News outlines the human cost of the war. In February alone, a minimum of 168 civilians were killed. At least 39 of the deaths recorded by the agency resulted from a February 27 airstrike on a busy market in Nihm, a contested district north of Sanaa. The strike was the deadliest coalition assault since another market, in the Houthi heartland of Sadah, was hit in September, killing 41. More than 3,000 civilians have been killed in the war to date; two-thirds of all casualties, according to the briefing, have resulted from airstrikes.

Civilian infrastructure has also been badly damaged during the war. "Factories, storage facilities, places of worship, civilian homes, and moving vehicles were among those targeted," the UNHCHR brief reads. "Targeting of protected objects was perpetrated by both parties to the conflict. According to IHL [international humanitarian law], such targeted or indiscriminate attacks against civilian objects may amount to war crimes or crimes against humanity."

In February, a UN panel of experts appointed by the Security Council recorded more than 119 aerial coalition attacks in which potential violations of international humanitarian law had been documented. A separate report co-written by the UN's Office for the Coordination of Humanitarian Affairs and Action on Armed Violence, a UK-based NGO that studies the effects of war, breaks down the impact of 124 attacks using explosive weapons since the war began: 5,239 people were killed or injured in the attacks, the authors believed, 4,493 of them civilians. Some 60 percent of the civilians casualties came from coalition airstrikes, the authors said.

Beyond the impact of conventional weapons on civilians, there is also the thorny issue of the coalition's use of cluster bombs, which has been documented by the UN, Amnesty, and Human Rights Watch. Cluster bombs are canisters that separate in mid-air, scattering dozens if not hundreds of "bomblets," which sometimes fail to detonate upon landing, leaving live munitions that look like toys on the ground. Given the wide area over which bomblets deploy, it's all but impossible to guarantee that cluster bombs will hit a specific target. Human rights advocates insist that the Convention on Cluster Munitions, an international agreement signed by 118 countries (though not by the US or Saudi Arabia), bans their use.

When coalition aircraft dropped cluster bombs on Sanaa, the Yemeni capital, it elicited an outcry. On January 6, residents of the Maaen district of Sanaa reported "aerial attacks consistent with cluster bomb use," Human Rights Watch reported, providing a photograph of the golf ball-sized BLU-63 bomblets dropped on the city and the CBU-58 canister used to disperse them. A trusted local source visited the strike site to confirm their use to VICE News, which has also seen internal UN correspondence that clearly states that the munitions were dropped on Sanaa.

VICE News first reported on the use of cluster bombs by the Saudi air force in Yemen in 2014.

In a press briefing in early March, the Saudi ambassador to the UN denied that the coalition had used cluster bombs, and the UK and US have both issued measured language expressing "concern over allegations" of their use, calling for a proper investigation.

VICE correspondent Ben Anderson holds a spent cluster bomb near the Razamat farm in Sadah, Yemen. (Photo by Peter Salisbury/VICE News)

During our latest shoot in Sadah, the Houthis' northern stronghold, we found fresh evidence that the Saudi-led coalition had used cluster munitions during the war. We stopped at a farm in the Nashour area of the province where Taleh al-Rezam, a retired military officer, lived with his family. Scattered along the hillside next to the farm was a collection of bright yellow canisters marked "BOMB FRAG BLU-97A/B 809420-30" that were attached to plastic parachutes. These were cluster munitions, manufactured in the US by the engineering firm Honeywell specifically for the American military, and probably part of a batch sold to Saudi Arabia by the US in the early 1990s. We also found the remnants of several of the canisters used to deliver the bombs, marked, "CBU 87B/B."

In 2013, the US authorized the sale of $640 million worth of cluster bombs to Saudi Arabia, with final delivery slated for December 2015. Textron, the manufacturer of the CBU-105 bombs sold to the kingdom, doesn't label them cluster munitions because they have a much lower failure rate than earlier iterations. These kinds of bombs are meant to be used in attacks on "strongpoints, bunkers, and dug-in facilities; armored and semi-armored vehicles; personnel; and certain maritime threats," according to a US document disclosing the planned sale. The new Textron bombs fall under the Convention on Cluster Munitions, however, making them illegal in the eyes of most rights groups.

And the coalition appears to have used the older, cruder versions even after scheduled delivery of the newer version.

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According to the UN panel, no party involved in Yemen's war is innocent. It found that the Saleh-Houthi alliance had "committed a systematic pattern of attacks resulting in violations of the principles of distinction, proportionality and precaution, including carrying out targeted shelling and indiscriminately aimed rocket attacks, destroying homes, damaging hospitals and killing and injuring many civilians." In Aden and Taiz, Houthi-Saleh forces have shelled civilian areas, seemingly indiscriminately; in Taiz, they continue to besiege the city, preventing food, water, and medical supplies from entering — actions that constitute war crimes.

They have also left a trail of live land mines in their wake and made liberal use of child soldiers. In Dahiyan, a small town in Sadah that has provided the Houthis with some of their top military leaders, we met a boy named Raei who said he was 14, though he looked like he had barely reached puberty. When we asked what he did, he replied, "I'm in the army."

International humanitarian law "is being violated on a daily basis by both parties," said Hassan Boucenine, Yemen country representative for the medical charity Médecins Sans Frontières (MSF), also known as Doctors Without Borders. "The only difference is that the extent, reach and firepower of the Houthis is far less than the coalition."

All parties to the Yemen war, he added, should be held to account for their actions.

Mike Newton, a former US soldier and military lawyer and one of the leading American authorities on international humanitarian law, quibbles with the way groups like Amnesty International and Human Rights Watch interpret humanitarian law. For human rights organizations, establishing what appears to be a widespread pattern of indiscriminate attacks that cause large numbers of civilian casualties is enough to prove the law has been broken. But under the complex legal framework involved in such cases, Newton says, rights organizations would have to have highly precise details from the ground and from inside the coalition operations center, which they almost certainly do not. There needs to be evidence that civilians are being targeted deliberately in order to say a war crime has been committed, in his view.

"It may be that there is systematically poor oversight" of the airstrikes, he said. But if the coalition investigates mistakes that have been made and works to improve its targeting while admitting its culpability, then it can avoid being charged with violations. Despite his skepticism of existing reporting, Newton agreed that the best way to settle the matter was to launch an independent international investigation into allegations of war crimes, as has happened with the Syrian war.

"I do think an independent investigation would be warranted, [involving] six or eight of the best law-of-war experts in the world," he said. "Real technical experts who are independent of governments or the UN."

The Saudis have steadfastly rebutted allegations of breaches of international humanitarian law during the war. At a press briefing in January, Brigadier General Ahmed al-Asiri, the Saudi-led coalition spokesperson, said that Saudi fighter aircraft are fitted with audiovisual devices that record the location of the jet and the target site, and relay information in real time about whether a strike has hit its intended target and any damage that was inflicted on surrounding areas.

All strikes alleged to be in violation of international humanitarian law are investigated, Asiri claimed. If an airplane had not been flying in the area of the alleged strike, allegations are discounted out of hand. (At a separate press briefing after the Wahijah wedding strike, Asiri denied that any coalition jets had been flying in the area at the time of the incident.)

Despite their protestations of innocence, the Saudis have repeatedly moved to block independent inquiries into allegations of war crimes in Yemen. In September of 2015, UN human rights chief Zeid Ra'ad al-Hussein implored member states to establish an international, independent human rights inquiry into possible crimes committed in Yemen by all sides. The Netherlands took up his call, circulating draft resolutions at the UN's Human Rights Council in Geneva to create a new investigative body on Yemen. The proposition enjoyed support from other UN missions, but soon came up against a concerted opposition campaign led by Saudi Arabia and its gulf allies.

Diplomats and human rights officials in Geneva revealed in detail how the Dutch resolution was first watered down during talks with the Saudis and ultimately blocked. It was replaced, we were told, with a Saudi text that merely authorized the UN's human rights office to provide technical assistance to an existing commission of inquiry being led by Yemen's Riyadh-based government in exile, and to monitor the situation on the ground and report to the Security Council. The Yemeni body, established in September 2015, is yet to announce that it has formally launched an investigation, although it did travel to Riyadh to visit the command and control center where coalition airstrikes are planned.

"As far as I can tell, it hasn't actually done anything yet," said a human rights researcher who has spoken with individuals closely monitoring the progress of the body and repeatedly approached the Yemenis on the matter. Zeid, the UN rights chief, had been expected to include critical language around the lack of progress made by the Yemeni body during a 10 March speech but instead said that he expected an update on their work in June.

Multiple UN officials and diplomats who requested anonymity in order to speak frankly told VICE News that there is strong resistance from Riyadh to any new resolution on Yemen that even obliquely references potential wrongdoing. In early March, Abdallah al-Mouallimi, the Saudi ambassador to the UN, held an impromptu press conference in New York where he told reporters that "senior" UN aid officials had said that there was no need for a suggested Security Council resolution on humanitarian access. (UN officials refused to confirm or deny his claims but said that he did not speak on their behalf.) Central to the tension is whether such a resolution contains explicit language on the protection of civilians and respect for international law, including an explicit call to end attacks on hospitals, events the coalition has been linked to on multiple occasions, UN officials told VICE News.

The site of an April 2015 coalition airstrike on a gas station in Sadah city. (Photo by Peter Salisbury/VICE News)

It's understandable that the Saudis would be so defensive and resistant to an independent investigation. But the position of the US and the UK, Saudi Arabia's top arms suppliers, is more problematic. They have provided both materiel and technical support for Riyadh's air war while denying direct involvement and expressing vague concern over the campaign's impact on civilians. British ministers have been particularly critical of the evidence being provided by those who claim war crimes may have been committed. In private briefings not directly authorized by their superiors, US officials have also questioned the quality of some of the reporting by organizations like Human Rights Watch and Amnesty.

Referring to a UN report alleging 100-plus coalition violations of international law at a parliamentary hearing in January 2016, Tobias Ellwood, the UK minister responsible for overseeing policy on the Middle East, said that the government took the allegations it contained "very seriously," but went on to argue that much of the purported evidence provided by human rights organizations was based on "hearsay and photographs." The UN experts, he said, despite admitting that he had not read their report, had not visited Yemen, instead basing their assessments on satellite imagery. The "media savvy" Houthis, Ellwood added, were also likely setting up the scenes of their own crimes to make them look like they had been perpetrated by the coalition.

"Evidence cannot be dismissed as hearsay when we have been on three different missions to the country," said Rasha Mohammed, Amnesty International's Yemen researcher, in response to Ellwood's criticism of the work of rights organizations. "The UK, US, and other governments do not hesitate to quote Amnesty International reports when they speak in favor of their objectives."

Since the beginning of the conflict, the US and UK have maintained that Saudi Arabia has the right to go to war in Yemen while insisting that a negotiated political process can be the only solution. While both countries routinely call for an investigation of apparent breaches of the laws of war in Yemen, they have hesitated to support an independent mechanism that might make that happen despite having enthusiastically supported such a mechanism to investigate allegations of war crimes in Syria.

The US was largely silent while the Dutch plan was being dismantled in Geneva, and Washington has yet to publicly endorse an independent investigation. Asked whether the government would support an independent commission of inquiry on war crimes in Yemen, the Pentagon referred VICE News to the State Department. State officials in turn simply highlighted their support for the Saudi version of the resolution and an internal inquiry Riyadh announced in January.

"We look forward to the Saudi government announcing the members of their investigative body soon and taking the steps necessary to ensure that it begins its work quickly," State Department spokesperson Mark Tone said.

"We want to see the Saudi Arabians hold thorough and conclusive investigations into alleged breaches of IHL," a British government spokesperson said. "We note that they have recently restated their commitment to complying with IHL and to pursuing investigations."

But as Asiri, the coalition spokesperson, has said, the aim of the new Saudi body established in January is not to investigate allegations of breaches of international humanitarian law. "Its primary goal is to confirm the precision of the procedures followed on the level of the coalition command," he told journalists at a January press briefing.

In other words, the body that the UK and US governments is backing to investigate allegations of wrongdoing is working to improve the quality of future strikes, not to publicly address potential mistakes.

Chris Jenks, a professor of law at Southern Methodist University and also a former military lawyer, said that an outside investigation wasn't required as long as "the countries conducting strikes are conducting and releasing investigations." But in Yemen, he said, "that isn't happening."

When asked in the past for proof that the coalition had not violated international law, Asiri and Saudi Foreign Minister Adel al-Jubeir have pointed to its Joint Combined Planning Cell, a command center where UK and US military advisers help the coalition plan its airstrikes. The center was established at the beginning of the war, apparently to ensure that the Saudi-led campaign met international standards. "We have British officials and American officials and officials from other countries in our command and control center," Jubeir told journalists in January. "They know what the target list is and they have a sense of what it is that we are doing and what we are not doing."

A recent interview with a former British minister suggests that the presence of UK personnel at the planning cell is being used to justify arms transfers to Saudi Arabia from a country that boasts, as the spokesman we spoke to reminded us, one of the most stringent arms exports regimes in the world. In an appearance on the UK current affairs show Newsnight last December, the former British business and industry secretary Vince Cable, who was in office when the war began, noted that he had temporarily blocked arms sales to Saudi Arabia on the basis of reports of human rights violations during the Yemen war.

Cable relented, he said, after British Defense Secretary Michael Fallon told him that the UK had military personnel "embedded" in coalition operations. "I was having to make a judgment on the basis of good faith," he remarked. "I was given assurances we had sufficient oversight of the bombing activity to make sure that international humanitarian law would not be compromised." Cable did not respond to calls and text messages from VICE News, but someone who discussed the matter in detail with Cable at the time said that he was concerned by the pressure placed on him to sign off on the arms sales largely on the basis that the Saudi kingdom is a so-called "priority market" for the UK.

The bloody remains of an abiyah belonging to a woman killed in the apparent coalition airstrike in Wahijah village. (Photo by Peter Salisbury/VICE News)

British and American officials are deep enough inside the process of target selection to judge that international law is not being broken, then, but they are sufficiently hands-off for officials to tell us that their personnel are not involved in directing or conducting operations in Yemen, nor are they involved in Saudi targeting decisions.

A senior US defense official with intimate knowledge of support for the Saudi intervention informed us that Pentagon lawyers are involved in determining whether strikes undertaken in operations that the US supports are lawful. But when the issue of potentially unlawful strikes is raised with the UK and US governments, officials dodge the question. After the Wahijah wedding strike, for example, the White House's National Security Council released a statement distancing the administration from the Saudi intervention, explaining in general terms that it was merely providing "targeting assistance" and was not involved in any final decisions.

Roger Cabiness, a Pentagon spokesperson, said that the US military is providing the Saudi-led coalition with "logistical support, intelligence sharing, general targeting processes and best practices, and other advisory support." US assistance has also included the vital delivery of nearly 28 million pounds of fuel for coalition aircraft. But American officials are at pains to reinforce the sense that they have no actual role in the command and control aspect the campaign.

"Final decisions on the conduct of operations [including the] final vetting of targets in the campaign are made by the members of the Saudi-led coalition, not the United States," said Cabiness.

"This is not our campaign in Yemen. We are not the intelligence provider for the Saudi-led coalition," said a senior US defense official who spoke on condition of anonymity. "There's a real limit to how much we can influence this."

The US and UK position, in which they internally report that the coalition is observing the law in airstrikes they oversee while publicly dodging questions on potentially unlawful strikes, is likely due to the fact that two distinct sets of airstrikes are taking place in Yemen, according to comments from American and British officials to VICE News that are corroborated by public briefings given by Asiri, the coalition spokesperson. (Asiri did not respond to a request for comment for this article.)

One kind of airstrike is pre-planned, based on satellite imagery, drones, reconnaissance aircraft, and human intelligence on the ground. The available intelligence is carefully parsed and a decision is made about whether the prospective strike site is an important military target and "unequivocally hostile," in Asiri's words. The potential collateral damage is also taken into account.

The other variety is a contingent or "dynamic" strike, which is based on real-time emerging intelligence from the air or the ground. The decision to launch such strikes, often on the basis of much thinner intelligence, is typically made within minutes rather than the hours or days that precede pre-planned strikes. According to multiple Western defense and diplomatic officials, dynamic strikes make up the majority of aerial assaults launched by the coalition.

The Joint Combined Planning Cell in which British and American officials are participating is entirely focused on pre-planned strikes. By some estimates, these account for as little as 20 percent of the total number of aerial actions taken by the coalition. (The US is only involved in a "small minority" of strikes, a US defense official confirmed to VICE News.) Dynamic strikes are said to be conducted at a different location from planned strikes and are completely separate from the joint planning cell.

The arrangement allows American and British lawyers to say that international law has not been broken, as far as they are aware, and it allows people like Cable's successor, Sajid Javid, to sign off on arms sales to Saudi Arabia. It also provides both countries with plausible deniability of UK or US complicity if the Saudi-led coalition is in fact found to be violating international law.

The Wahijah attack, for example, would make more sense if it were a dynamic strike: a group of Houthi fighters are seen by the coalition, enter and leave the village as large numbers of people converge on the two wedding tents. A hasty decision is made, and dozens of people are killed in a strike. Or, Houthi fighters are present at the wedding, but in small numbers that do not justify launching an airstrike in an area thick with civilians. The wrong call is made, and dozens of people die.

This is also where human rights organizations clash with military lawyers like Newton, since they argue that the regular occurrence of such mistakes amount to war crimes. Newton sees the issue as being knottier — as long as the coalition is working to avoid past mistakes, it is not on the hook for them. This might explain why US and UK officials are seemingly content with the current Saudi setup, where they try to improve the accuracy of their strikes rather than dwell on past mistakes.

American and other senior Western government officials told VICE News that the quality of the intelligence collected by the Saudis is not up to the standards that the US would usually require, and that the coalition has yet to reach an acceptable standard in its decision-making process with regard to dynamic strikes. The coalition has launched more strikes in Yemen than the US-led anti-Islamic State coalition has launched in Syria and Iraq, where US officials have been forced to admit a number of mistakes.

"As a matter of policy, we do not discuss matters and methods of analyzing and gathering intelligence," Cabiness, the Pentagon spokesperson, told us when we asked about the quality of intelligence and the coalition's ability to launch dynamic strikes with it. "The US is confident that the intelligence and advisement we relay to Saudi Arabia and other coalition members is sound and provides them the best options for military success consistent with international norms and specifically mitigating the potential for civilian casualties."

A British government spokesperson, speaking on behalf of the different government departments, did not respond to questions on the quality of the intelligence being used to plan strikes.

Despite the toll of the Saudi-led campaign, neither the US nor the UK has indicated that their support for Riyadh has diminished over the past year, although the senior US defense official did concede to us that he thought the loss of civilian lives was "a real loser strategically" for Saudi Arabia.

In the wake of its nuclear deal with Iran, the Obama administration is struggling with an internal need to be conciliatory toward Saudi Arabia under a new king who has taken a more aggressive approach to the country's role in the region. Salman bin Abdulaziz ascended to the throne in January of 2015, just two months before the Yemen war, during a period of tensions with the US over the Iran nuclear deal, and he does not take criticism well.

"The Saudis are totally unwilling to listen to anyone criticizing their foreign policy right now," said Nabeel Khoury, a former American diplomat and Middle East specialist who was based in Yemen between 2004 and 2007. "They feel so strongly, and this leadership is so committed and convinced that what they are doing is right, that they are not entertaining advice.

From the American point of view, Khoury adds, the Yemen war has gone on too long, produced too little, and done too much damage to the Yemeni people. "But on the motive of the Saudi war in Yemen, the US perspective doesn't seem to be that much different," he says. "This is a Houthi-instigated war supported by Iran, and that the prospect of Houthi dominance in Yemen and Iran's role in Yemen which would only grow. The US thinks that would be unacceptable."

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The current approach also fits into a position articulated by President Obama in a recent with The Atlantic's Jeffrey Goldberg: the US needs its regional allies to step up to the plate. "Philosophically, it is something that they have been pushing towards for some time," says Stephen Seche, a veteran US diplomat and former ambassador to Yemen, now an analyst at the Washington, DC-based Arab Gulf States Institute in Washington. "President Obama has said yes we have a responsibility but we do not need to be the point of the spear every time. We are not going to be the ones who are dictating the terms of the coalition or leading it.

US defense officials have long wished to see the Saudis use their arsenal in combat, and see the war as a training exercise for a potentially important military partner. Constrained by domestic oversight and budgets, the US military is now outsourcing some aspects of regional wars to Gulf states, Saudi Arabia in particular, as a reasonable if not attractive workaround.

The senior defense official noted that Gulf countries are fighting on their own for the first time in many decades. This, the official said, was "something we've dreamed of."

For the UK government, however, there are still the complications of the country's stringent arms export laws, which theoretically prevent it from providing support to buyers whose conduct risks violating humanitarian law.

"There has been a lot of work by HRW, Amnesty, the UN panel, to demonstrate the damage, find out what has occurred," said Roy Ibitser, an arms control expert at the UK charity Saferworld. "A lot of deliberate, careful work has been done here using GPS coordinates, satellite imagery, photos of fragments, that produces a strong evidence base. This might not stand up in a court of law. But that isn't the way the [UK arms export] law works. It talks about risk, the risk that equipment could be misused in the future. And if you talk to just a reasonable human being whether there is a risk that these weapons might be used in indiscriminate attacks in Yemen, the answer is blindingly obvious."

Saudi Arabia is publicly mulling a more active role in the fight against IS in Syria, and, having broken the seal on its American and British munitions, may soon choose to enter into other conflicts in the region. The Yemen war doesn't seem to have changed British or American minds about having the kingdom taking the lead in combat — both Obama and Cameron have provided enthusiastic backing for the idea.

"If you think very cynically, Saudi Arabia is getting real training," Khoury said of its Yemen war. "It has been a training exercise for the Saudis on two fronts: giving their pilots an opportunity to engage in live combat, and in trying to coordinate diverse forces under their leadership."