A cataclysmic war is taking shape in Yemen, one that pits nearly all of Washington’s key allies in the Middle East against Iran and its proxies in a fight that could quickly spin out of control.

A Saudi-led bombing campaign already has begun and troops from Egypt and some other countries may soon intervene on the ground.

All of this was done, according to a Saudi source who is part of the inner circle in Riyadh, without significant American involvement. “We have done this on our own,” this source told The Daily Beast. While the U.S. has a handful of people in a Saudi operations center, the source noted that this coalition was pulled together and went into action without the U.S. leadership that characterized, for instance, the Desert Shield/Desert Storm operations of 1990 and 1991. The Saudis have dubbed this operation “Decisive Storm.”

Ten Arab countries are involved, including not only those of the Gulf, but Jordan, Egypt, Morocco, and even Sudan. Turkey—which has the second-biggest military in NATO, after the United States—may be the next to join. “The Iranian influence has to be challenged,” said this Saudi source.

But the question now, at the start of what could be the start of the next great Middle Eastern war, is: How far will Washington really go back its old allies? And will it risk alienating its new negotiating partner in Tehran?

The Obama administration finds itself in a position that is full of contradictions and almost completely untenable. It is offering some behind-the-scenes intelligence support to the Saudi-led anti-Iranian offensive in Yemen, but at the same time it is using American airpower to reinforce an offensive by Iranian-backed forces fighting the so-called Islamic State in Iraq. Most significantly, the Obama administration is trying to negotiate a controversial deal to contain Tehran’s nuclear ambitions.

“You couldn’t make this stuff up,” one veteran U.S. diplomat said with bitter irony.

The Arab states now arrayed against Iran in Yemen have warned repeatedly—as, indeed, has Israel—that if Iran is able to obtain nuclear weapons its ambition to dominate the region will be virtually impossible to contain. And recent events, in the view of the Saudis and their allies, prove that Iran is on the move even without the backup the Bomb would give it.

In Lebanon, Syria, Iraq, and Yemen the gains of Iranian-backed militias have been such that the architect of this expansionist policy, Quds Force Commander Qasem Suleimani, is being touted as a contender for the Iranian presidency in 2017. Washington, reacting to events rather than shaping them, has been wrong-footed again and again.

Ironically, only last year President Barack Obama cited Yemen as a model for the kinds of policies he thought the United States should pursue in its war against al Qaeda affiliates. But the U.S. drones, American Special Operations Forces, and local commandos trained by the United States were so heavily focused on their fight against al Qaeda in the Arabian Peninsula that they failed to perceive the rising power of Iran and the Shiite Houthi rebels that it supported.

Over the last few days, U.S. forces in Yemen have been evacuated in haste, reportedly leaving behind troves of sensitive documents.

In an interview with The Daily Beast, Senator Richard Burr, the chairman of the Senate Intelligence Committee, underscored the chaotic development of events on the ground in Yemen. “We’re totally out,” he told our correspondent Tim Mak. “Yemen is going to be, in the president’s own words, a ‘model,’ [but] not of success, [instead] of absolute failure of our foreign policy.”

Since late last year, Tehran’s backing for the Houthi rebels has been increasingly obvious. They took control in the capital Sanaa in January, ousting President Abed Rabbo Mansour Hadi from his palace there, and they have been closing in on his displaced government in the southern Yemen city of Aden. Hadi is now reportedly in the Saudi capital, Riyadh.

Photos: Rubble and Grief—On the Ground in Yemen

Scott Atran, a Mideast analyst with Artis Research who has worked closely with U.S. government agencies as a consultant, tells The Daily Beast, “There was no preparation for this and no understanding that I can see within senior U.S. policy circles that the wider Sunni-Shia conflict is what it is all about. The Saudis feel they are fighting for their very existence.”

Indeed. From the Saudi point of view, Iran is gaining strength in Syria, where it is the embattled Assad regime’s most important ally, in Iraq, where it is propping up the mainly Shiite central government, and now in Yemen. All of these countries are on Saudi Arabia’s borders, and, what is more, to the extent that pro-Iranian Shiite forces appear to be gaining momentum, that threatens to disrupt the fragile equilibrium in the oil-producing Eastern Province of Saudi Arabia, which has a majority Shiite population. Partly because of fears the crucially important production from Saudi Arabia may be disrupted, oil prices rose dramatically on Thursday.

“The Saudis are scared right now. They’re worried about Iran,” a U.S. official in contact with governments in the region told The Daily Beast. Riyadh may have notified the United States about their airstrikes, but they made it clear that they weren’t waiting for the American military to come to their aid, the official said.

The Americans should “join the team” fighting Iran in Yemen, a former senior official in the U.S. intelligence community told The Daily Beast. “We should have helped Hadi long ago against his most significant threat [the Houthis], and not just against AQAP. Had we done so, we would not be where we are now.”

The Saudis are making a strong public showing both of the military operations and their support for the Hadi government. Prince Muhammad bin Salman, the Saudi defense minister and King’s son, visited the border region with Yemen this week. Just 34 years old, he is the youngest defense minister in the world and is “a rising star” within the Saudi government, Bruce Riedel, a former CIA officer and senior fellow at the Brookings Institution, told The Daily Beast. The prince also reportedly received ousted Yemeni president Abd-Rabbu Mansour Hadi in Riyadh on Thursday, after Hadi fled Yemen on Wednesday in the face of the Houthi onslaught.

As Riyadh portrays the offensive, the purpose is to let not only Iran but the leaders of al Qaeda and the so-called Islamic State know that Riyadh and its allies mean business. “Extremists must know we are ready to fight,” he said. “This is a nucleus of the Arab force to stand against Islamic extremism,” he claimed optimistically.

Riyadh’s hope, according to this source, is that the Houthis and their Iranian backers will be forced to engage in serious negotiations about Yemen’s future.

“As a starting point, we are doing something to stop the Houthis from going to Aden,” the source said. “But once you go into this sort of potential quagmire you have to consult all the options. The Houthis were really surprised by the [Saudi-led] assault and the ferocity of it.”

But the Saudis and their partners may not be able to maintain a military operation against the Houthis for long. “The Saudis don’t have a sizable military force that can launch expeditions in Yemen, which limits their military capability,” the official said. If the Saudi coalition cannot keep up the attack on the Houthis, the Americans may have little choice but to join the fight, the official said.

Iranian Foreign Minister Mohammad Javad Zarif told an Iranian-owned television channel that the Saudi-led bombing would only lead to further loss of life. "Military action from outside of Yemen against its territorial integrity and its people will have no other result than more bloodshed and more deaths,” said Zarif, who is considered to be a moderating force in the Iranian government and is central to the ongoing nuclear negotiations. He called for an "urgent dialogue” among the Yemeni factions "without external interference.”

It seems, in fact, far too late for that.

— with additional reporting by Shane Harris