WASHINGTON (Reuters) - The Pentagon, facing accusations that a coalition air strike may have killed scores of civilians in the Iraqi city of Mosul, said on Monday it was not loosening its rules of engagement in the fight against Islamic State but that resources to investigate claims were limited.

Smoke rises from clashes during a battle between Iraqi forces and Islamic State militants in the city of Mosul. REUTERS/Youssef Boudlal

Eyewitnesses from Mosul and Iraqi officials have said last week’s strike on Islamic State targets may have collapsed homes where rescue officials say as many as 200 people were buried in the rubble.

The U.S. military does not intend to change the way it carries out strikes, even as the fighting in Mosul enters more densely populated areas, Colonel John Thomas, a spokesman for U.S. Central Command, told reporters.

“General Votel is not looking into changing the way we operate other than to say our processes are good and we want to make sure we live by those processes,” Thomas said.

General Joseph Votel heads Central Command.

“There (are) only so many people dedicated to this who really have the expertise to get us where we need to be,” Thomas added.

The Mosul strike, if confirmed, would be one of the deadliest single incidents for civilians in recent memory in any major conflict involving the U.S. military, which prides itself on efforts to limit civilian fallout.

Thomas said the assessment is looking at 700 videos from the area over a 10-day period.

“We didn’t have any reports internally where we thought we had killed any civilians. We saw the reports come out just like, I think, like everybody else,” Thomas said.

Rescue workers are still searching the site of the March 17 explosion in Western Mosul, where one health official said 160 bodies had been recovered. Iraq’s military says 61 bodies have been pulled out so far.

The civilian death toll has increased in the more densely populated west of Mosul as militants have used homes for cover.

“The absolute default in every building should be that there are going to be civilians present,” said Jay Morse, a senior military adviser at the Center for Civilians in Conflict, a U.S.-based advocacy and research group.

Iraqi forces have discussed new tactics, which a U.S. military official said might include opening a second front and trying to isolate the Old City.

Earlier on Monday, U.S. Defense Secretary Jim Mattis appeared to back the way the United States carries out strikes.

“There is no military force in the world that has proven more sensitive to civilian casualties,” Mattis said before a meeting with his counterpart from Qatar.

“We go out of our way to always do everything humanly possible to reduce the loss of life or injury among innocent people. The same cannot be said for our adversaries,” he said.

The coalition has said that investigating the allegations in Mosul is a priority and it is assessing the credibility of conflicting reports.

The military has also opened an investigation into a strike in northern Syria this month believed to have killed nearly 50 people and is probing allegations that another strike hit a school near Raqqa.