Jim Michaels

USA TODAY

The U.S. military is investigating reports that more than 100 civilians were killed in a coalition airstrike last week in Mosul, where U.S.-backed Iraqi forces are clearing the city of Islamic State militants.

If confirmed, it would be the largest civilian casualty incident in the coalition air campaign in Iraq and Syria, which is more than two years old.

The coalition said in a statement Saturday that the assessment is focused on a March 17 airstrike made at the request of Iraqi security forces in the area where the allegations surfaced. The coalition said it opened an initial "civilian casualty credibility assessment" to determine the validity of the reports.

Iraqi teams picking through the rubble of several buildings destroyed in the Al-Jadida neighborhood in west Mosul uncovered dozens of bodies. Iraq’s Civil Defense Department said workers discovered the bodies once it was safe to re-enter the area.

The Islamic State, also known as ISIS, often uses civilians as human shields and rigs entire buildings to explode. The militants frequently store explosives inside buildings and an airstrike could have set off a “secondary” explosion.

Iraqi security forces have been aggressively battling militants inside west Mosul, a densely packed neighborhood of narrow streets and alleyways.

It is generally difficult to use artillery and air support during urban combat. But the U.S.-led coalition has kept a steady pace of airstrikes during the Mosul offensive, using precision munitions and surveillance video to vet requests for air support.

Airstrikes have been so precise they have targeted individual snipers in buildings in Mosul, providing further confidence to Iraqi forces moving through the city.

The offensive to retake Mosul began in October, and the east side of the city is now largely cleared of militants. The pace of the offensive in the west has been moving rapidly, at least in part because of continued coalition airstrikes, according to the Pentagon.

The coalition said it would continue to support Iraqi forces as they move through the city. The coalition conducted a number of strikes Friday against Islamic State targets, including enemy fighting positions, mortars and a heavy machine gun team.

“Our goal has always been for zero civilian casualties, but the coalition will not abandon our commitment to our Iraqi partners because of ISIS's inhuman tactics terrorizing civilians, using human shields, and fighting from protected sites such as schools, hospitals, religious sites and civilian neighborhoods,” the coalition statement said.

The coalition air campaign has been among the most tightly regulated in history. Most strikes require approval by a general officer after planners examine intelligence, video and other evidence to ensure the target is legitimate and that there are no civilians within range.

It is not clear what went wrong or even if the coalition was responsible, but the incident could trigger a debate over how much control the administration should exercise over the military campaign.

The Trump administration has indicated it wants to give commanders more leeway in making battlefield decisions, even though the White House has not changed any current authorities or rules of engagement.

“One thing they’re already doing … is giving commanders in the field much greater latitude as far as military operations,” Sen. John McCain, the Republican chairman of the Armed Services Committee, said recently.

Contributing: Igor Kossov in Irbil, Iraq.