The Pentagon's fight against the Islamic State has grown increasingly aggressive since late fall and includes higher levels of allowable civilian casualties in the bombing campaign to target militants and their cash supplies, according to interviews with military officials and Pentagon data.

Since last fall, the Pentagon has delegated more authority to the commander of the war, Army Lt. Gen. Sean MacFarland, to approve targets when civilians could be killed. Previously, authority for missions that ran a higher risk of killing innocents had been made by higher headquarters, U.S. Central Command. Seeking approval from above takes time, and targets of fleeting opportunity can be missed.

Six Defense Department officials, all speaking on condition of anonymity because they were not authorized to describe how Islamic State, also known as ISIS, targets are selected and attacked, described a sliding scale of allowable civilian casualties, based on the value of the target and the location. For example, a strike with the potential to wound or kill more civilians would be permitted if it prevented ISIS fighters from causing greater harm

Before the change, there were some very limited cases in which civilian casualties were allowed, the officials said. Now, however, there are several targeting areas in which up to 10 civilian casualties are permitted. Those areas shift depending on the time, location of the targets and the value of destroying them, the officials said.

The riskiest missions require White House approval, said one official, who is closely involved with current targeting plans.

The officials all say commanders go to great lengths to avoid killing innocents. They attack at night, for example, when buildings are less likely to be occupied. They select bombs that spew fewer deadly fragments and direct laser-guided bombs away from targets when civilians stray too close to ground zero. Military lawyers oversee operations to ensure laws of war are followed.

The increased tolerance for civilian casualties dovetails with the revised strategy Defense Secretary Ash Carter announced in October — the focus on recapturingRamadi, Iraq, mounting more raids to capture or kill ISIS leaders and adding pressure to Raqqa, Syria, the capital of ISIS's self-proclaimed state.

Col. Sean MacFarland on patrol in Ramadi. Photo by U.S. Army.

× Fear of missing out? Sign up for the Early Bird Brief - a daily roundup of military and defense news stories from around the globe. Thanks for signing up. By giving us your email, you are opting in to the Early Bird Brief.

Lt. Gen. Sean MacFarland, as a colonel in Iraq in 2007, commands U.S. forces against ISIL.

Photo Credit: U.S. Army

Among the issues commanders consider before attacking is the target's "non-combatant value." A value of zero means it can be hit with no chance of civilians being killed — think of an ISIS machine gun emplacement in the desert.

The value rises in urban areas such as Ramadi, which Iraqi forces, backed by U.S.-led airpower, seized from ISIS in late December. Pockets of Ramadi and other areas of intense fighting have had non-combatant values of 10 or more, meaning that attacking them carries the probability of 10 civilian deaths, said the most senior of the six Defense officials. The area could be as small as a city block and permission to hit it could last for a matter of hours.

MacFarland, who took command in September, has also focused on ISIS's source of income and stores of cash — oil infrastructure and banks. Black-market oil had been a key source of illicit income need to finance its operations and pay fighters. Civilians work on oil rigs or visit banks, forcing commanders to weigh the strategic value of destroying them with the probability that civilians will be killed.

Military planners can mitigate the risk by dropping leaflets, as they did last fall, warning drivers of tankers with illicit oil to flee before blowing them up. A bank could be struck at night, with the least-lethal bomb, at an angle that minimizes damage to nearby buildings, the senior official said.

The more aggressive approach has been reflected in the bombing statistics released by the Pentagon.

In November, pilots in the U.S.-led coalition had dropped 3,227 bombs in Iraq and Syria, a record number for a single month and more than twice as many as they had used in November 2014. Since then, the totals for bombs dropped per month eclipsed the previous year. In March, pilots dropped 1,982 bombs compared with 1,685 in March 2015, an 18 percent increase.

Minimizing civilian casualties

Although the military acknowledges publicly that its airstrikes have killed or wounded 26 civilians by accident, two officials, one currently involved in targeting and one former senior officer, say more innocent civilians may have died from the more than 40,000 bombs that have been dropped since the war began in August 2014.

By destroying nearly 6,000 buildings with bombs since the war began it's a virtual certainty that the civilian toll is higher than 26, said a senior Defense official who is briefed daily on the war's developments. Even if it is 10 times higher, the official said, it would be exceptionally low and reflects the U.S. military's commitment to protecting the innocent.

Central Command, which oversees the war, investigates reports of civilian casualties. Claims, even tweets, are matched against missions flown to determine if coalition aircraft had conducted bombing runs nearby. Video from drones and other aircraft track every bomb dropped, one of the six Defense officials said. If the report is deemed credible, investigators assess whether strikes comply with the laws of war and that proper precautions were taken.

One such incident occurred on July 4, 2015, near Raqqa, Syria. Airstrikes destroyed 16 bridges there. A bomb also killed a civilian driving a tractor trailer.

Civilian deaths caused by Iraqi military operations, which occur jointly with the American-led bombing effort, are not counted, the senior official said.

In more than 15 years of bombing Afghanistan and Iraq, the Pentagon has put a premium on avoiding civilian casualties. The laws of war, military professionalism and the American public's aversion to killing innocents demand care and precision. Also, destroying the lives and property of non-combatants is considered self-defeating when the protection of local civilians is a priority.

Airstrikes are considered deliberate or dynamic. A deliberate strike can be planned for — a bank in Mosul for example. With time, commanders can choose the best time and weapon to minimize chances civilians will be harmed. Commanders, one official with experience in targeting said, are in a rush to get it right — not just to strike. No civilians were hurt or killed in the more than 100 tons of explosives dropped over two months of fighting, the senior official said.

A complicating factor for commanders is the urgency of the time-sensitive mission, also known as a dynamic target. For example, an ISIS militant attacking Iraqi troops from a rooftop machine gun nest in Ramadi is a legitimate, dynamic target. Commanders must judge if killing him puts residents on lower floors at risk of injury or death.

Soon after bombing extended to Syria in September 2014, commanders had pinpointed the seven buildings in Raqqa that ISIS used for headquarters, said a recently retired senior officer involved in targeting. The buildings, legitimate military targets, were deemed off limits because they were too close to civilians to be destroyed without wounding or killing innocent bystanders, the former officer said.

Targeters pore over hours of video from spy aircraft of potential bomb sites to determine when civilians are least likely to be nearby, the former officer said. Determining the "pattern of life" at the target can trigger the decision to bomb or not to bomb.

ISIS leaders have complicated targeting by flying their black flags over residential buildings, inviting airstrikes so that they can blame the U.S.-led coalition for killing civilians, the senior official said.

The vast majority of strikes in Iraq and Syria belong in the dynamic category. It's difficult to determine if innocent civilians have been trapped in buildings damaged or destroyed in dynamic strikes, the senior official said.

The calculation for civilian casualties changes based on the strategic value of a target and the local population's sensitivity to foreign military presence, said the recently retired officer said.

During the surge in Iraq beginning in 2007, the non-combatant value for some targets was as high as 26 people, said the former officer. In Afghanistan, during the surge of troops there in 2010, the value was nine.