FILE - In this Friday, March 24, 2017, file photo, residents carry the body of several people killed during fighting between Iraq security forces and Islamic State militants on the western side of Mosul, Iraq. Iraqis in the northern city of Mosul are still burying their dead after a U.S. airstrike allegedly killed more than 100 people last week, and rights groups are expressing alarm over a recent spike in civilian deaths. Iraqi officials have defended their conduct in the war against the Islamic State group, and their advice to civilians is to shelter in place as U.S.-backed forces seek to drive the extremists from their last urban stronghold in the country (AP Photo/Felipe Dana)
FILE - In this Friday, March 24, 2017, file photo, residents carry the body of several people killed during fighting between Iraq security forces and Islamic State militants on the western side of Mosul, Iraq. Iraqis in the northern city of Mosul are still burying their dead after a U.S. airstrike allegedly killed more than 100 people last week, and rights groups are expressing alarm over a recent spike in civilian deaths. Iraqi officials have defended their conduct in the war against the Islamic State group, and their advice to civilians is to shelter in place as U.S.-backed forces seek to drive the extremists from their last urban stronghold in the country (AP Photo/Felipe Dana) Credit: Felipe Dana

Baghdad — U.S. airstrikes probably played a role in the deaths of dozens of civilians in Mosul earlier this month, U.S. and Iraqi military officials acknowledged on Tuesday, but they denied the rules for avoiding civilian casualties have been loosened despite a recent spike in civilian casualties.

Speaking from Baghdad to reporters at the Pentagon, the top commander of U.S. forces in Iraq said an ongoing investigation may reveal a more complicated explanation for the March 17 explosion that residents say killed at least 100 people, including the possibility that Islamic State militants rigged the building with explosives after forcing civilians inside.

Army Lt. Gen. Stephen Townsend said a recent spate of civilian casualties in Mosul was “fairly predictable” given the densely populated urban neighborhoods that the ISIL fighters are defending against Iraqi government troops. But the civilian deaths cannot be attributed to any loosening of American military rules of combat, he said, and Washington hasn’t decided to tolerate greater risk of civilian casualties in U.S. airstrikes.

Amnesty International on Tuesday said the rising death toll suggested the U.S.-led coalition wasn’t taking adequate precautions as it helps Iraqi forces try to retake the city.

Townsend acknowledged the U.S. conducted multiple airstrikes in the area of the explosions. That, coupled with initial inquiries done by U.S. technical experts who visited the scene, led him to say: “My initial assessment is that we probably had a role in these casualties.”

But Townsend said the type of munitions used by the U.S. in the airstrikes should not have been able to bring down the entire building, raising questions about the level of American involvement. He said U.S. officials were assessing the possibility that ISIL forced civilians to gather there to act as human shields or to lure the U.S. into attacking.

“It sure looks like they were,” Townsend said. Another possibility that was being examined was that the militants filled the building with explosives, he said.

In the most extensive U.S. explanation of what is known about the event, Townsend stressed that no one should think it was a deliberate U.S. act. “If we did it — and I’d say there is at least a fair chance we did — it was an unintentional accident of war,” he said.

Iraq’s ministry of defense also blamed ISIL for the high civilian death toll.

“As our forces advanced toward that area to liberate it, the explosive-laden tanker truck headed toward our advancing troops, it was targeted by an airstrike which led to a huge explosion. The explosion damaged number of buildings, including the one where ISIL crammed about 130 civilians,” said the ministry’s spokesman, Brig. Gen. Yahya Rasool.

ISIL planned the incident to “impact the civilians, to inflame the public and to convey a wrong message to the world that the joint forces and the international coalition are behind the killing and bombings,” Rasool said.

The fight for western Mosul began in February after Iraqi security forces pushed ISIL out of the eastern side of the Tigris River city. In recent weeks, ISIL defenders have packed into neighborhoods with narrow streets and trapped civilians, Townsend said.

“It is there that the enemy has invested two-and-a-half years of defensive preparations,” he said, calling it the “toughest phase” of the war.

“I think that’s really the explanation for the civilian casualties,” Townsend added.