WASHINGTON — The senior United States commander in Iraq said Tuesday that an American airstrike likely triggered the collapse of a building in Mosul that killed more than 100 civilians this month, but indicated that an investigation would also examine whether the attack set off a larger blast from explosives set by militants.
It was the fullest acceptance of responsibility by an American commander since the March 17 strike.
“My initial assessment is that we probably had a role in these casualties,” said Lt. Gen. Stephen J. Townsend, who commands the American-led task force that is fighting the Islamic State in Iraq and Syria. But he asserted that “the munition that we used should not have collapsed an entire building.”
“That is something we have to figure out,” he added.
With an increase in reports of civilian casualties from the American bombing of Islamic State targets in Iraq and Syria, some human rights groups have questioned whether the rules of engagement had been loosened since President Trump took office.
Pentagon officials said this week that the rules had not changed. But General Townsend said on Tuesday he had won approval for “minor adjustments” to rules for the use of combat power.
He insisted, however, that they were not a factor in the Mosul attack.
General Townsend said the steps were taken to speed up the process of providing airpower to support Iraqi troops and American Special Operations advisers at the leading edge of the offensive to recapture Mosul from the Islamic State. Among the changes were to “decentralize” decision-making, he said.
General Townsend did not describe the changes in detail, but cast them as a return to the military’s standard offensive doctrine following the “very centralized” approach he said was initially put in place after President Barack Obama sent American forces back to Iraq to combat the Islamic State.
Maj. Gen. Maan al-Saadi, an Iraqi special forces commander, told The New York Times his men had called in the American airstrikes that caused the civilian deaths in Mosul.
General Townsend said that he did not have information on the Iraqi officer’s specific role, but explained that any American airstrike requested by the Iraqis would also need to be approved by American forces.
“If he said his guy was calling for fire, it could have been,” he said. “Now how that works is that they don’t call directly to a U.S. fighter overhead and suddenly a U.S. fighter is rolling in on their grid coordinates.”
Iraqi forces have been eager to receive American airpower as they take on the toughest phase of the more than five-month battle to retake Mosul. American officials have said that 500 Iraqi troops were killed and some 3,000 wounded in taking the eastern half of the city.
General Townsend said that the battle for the west of the city was even more difficult because of what he called its “claustrophobically close terrain” of narrow streets and buildings, repeating several times that the house-to-house fighting was the most intense urban combat since World War II.
Adding to the challenge is a factor he did not mention: the decision by Iraq’s governments to urge Mosul’s residents to shelter in place instead of trying to flee. When American troops retook Falluja in 2004, the fierce fighting there took place in a city that had already been abandoned by most civilians.
Brig. Gen. Matthew Isler, an Air Force officer who serves as deputy to General Townsend, has been put in charge of the investigation into the Mosul episode. A team of American experts has visited the site to collect evidence to determine what caused the significant loss of civilian life.
“My initial impression is the enemy had a hand in this, and there’s also a fair chance that our strike had some role in it,” General Townsend said in a briefing. “I think it’s probably going to play out to be some sort of combination. But you know what, I can’t really say for sure and we just have to let the investigation play out.”