WASHINGTON — The U.S.-led military coalition in Iraq said Saturday that an initial review of recent airstrikes in Mosul, the Islamic State's last stronghold in Iraq, had confirmed that the strikes hit a site where scores of civilians were killed.

The inquiry, military officials said, found that a building had collapsed a few days after strikes by U.S. forces. U.S. officials are seeking to determine whether the airstrikes brought down the building, leaving many Iraqis dead, or the Islamic State used the strikes as an opportunity to detonate an explosive in the building.

The Pentagon had acknowledged Friday that it was investigating reports that its airstrikes had caused deaths in Mosul. The next phase of the investigation, military officials said, is likely to take about three weeks.

The March 17 airstrikes — which Iraqis said had led to the deaths of possibly 200 people — could have produced among the highest civilian death tolls in a U.S. air mission since the U.S. invaded Iraq in 2003.

The reports of heavy civilian casualties have come at a critical point in the military campaign to defeat the Islamic State. Iraqi officials said that the Trump administration had appeared to loosen restrictions on the rules of engagement, making it easier for the Iraqis to call in airstrikes. The Iraqis had been frustrated by the Obama administration's deliberate approach.

Capt. Jeff Davis, a Pentagon spokesman, said that the rules had not been loosened.

The coalition said in a statement Saturday that the airstrikes had been conducted "at the request of the Iraqi security forces," and that it believed it was hitting Islamic State fighters and equipment.

"The coalition respects human life, which is why we are assisting our Iraqi partner forces in their effort to liberate their lands from ISIS brutality," the statement said. "Our goal has always been for zero civilian casualties, but the coalition will not abandon our commitment to our Iraqi partners because of ISIS' inhuman tactics terrorizing civilians, using human shields, and fighting from protected sites such as schools, hospitals, religious sites and civilian neighborhoods."

It added: "Coalition forces work diligently and deliberately to be precise in our airstrikes. Coalition forces comply with the Law of Armed Conflict and take all reasonable precautions during the planning and execution of airstrikes to reduce the risk of harm to civilians."

The civilian deaths occurred in the recently liberated neighborhood of Mosul Jidideh, and reports of mass casualties began emerging Thursday, six days after the coalition said it had struck the area. That lapse may have been a result of delays in getting rescue workers to the area, some of whom traveled from Baghdad, 250 miles away.

Iraqis continued Saturday to pull bodies from the rubble, as families held hastily arranged funerals for the victims, some of whom were buried in mass graves, shrouded by blue tarpaulins, according to photographs and videos shared on social media.

In one video, Basma Basim, head of Mosul's provincial council, stood in front of destroyed buildings where the strikes occurred and said that dozens "of innocent women, men, old men and children's bodies, are in these homes and shops behind me — we couldn't save them."

She added, "All the men I met had a wife, sister or children buried under the rubble, at least 20 persons died for each."

The battle for Mosul, now in its sixth month, has taken a heavy toll on civilians, with the Islamic State gathering civilians to use as human shields and, lately, with reports of growing numbers of deaths from airstrikes.

The Iraqi Observatory for Human Rights, a monitoring group, said in a statement that more than 3,800 civilians had been killed in the battle for western Mosul, which began in January. On the eastern side of the city, which was declared liberated in January after months of fighting, 2,190 civilians were killed, the group said.

In a statement Saturday, Lise Grande, the United Nations' top humanitarian official for Iraq, said, "We are stunned by this terrible loss of life and wish to express our deepest condolences to the many families who have reportedly been impacted by this tragedy."

She added: "Parties to the conflict — all parties — are obliged to do everything possible to protect civilians. This means that combatants cannot use people as human shields and cannot imperil lives through indiscriminate use of firepower."

Iraq's Ministry of Defense, which works closely with the U.S. military, broke two days of silence Saturday when it said that it was opening an investigation into the civilian deaths. At the same time, the speaker of the Iraqi parliament, Salim al-Jubouri, ordered commanders of Iraq's security forces to give lawmakers a report on the matter and to appear before the assembly.