BAGHDAD >> An airstrike targeting Islamic State militants in the Iraqi city of Mosul that witnesses say killed at least 100 people was in fact launched by the U.S. military, American officials said today.

U.S. officials did not confirm the reports of civilian casualties but opened an investigation. In the days following the March 17 airstrike, U.S. officials had said they were unsure whether American forces were behind the attack.

The statement issued by the U.S.-led coalition said the airstrike had been requested by Iraqi security forces to target IS fighters and equipment “at the location corresponding to allegations of civilian casualties.” U.S.-backed government troops were fighting IS forces in that area of western Mosul, the statement said.

The coalition said it takes all allegations of civilian casualties seriously and a formal Civilian Casualty Credibility Assessment had been opened to determine the facts surrounding this strike and the validity of the allegation of civilian casualties.

“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 said.

Altaf Musani, representative of the World Health Organization in Iraq, told the Associated Press in the Jordanian capital of Amman that the organization’s priority was quick treatment for those wounded.

“It is our understanding that there was an incident and we have worked with the local health actors and they have confirmed more than 100 are dead,” Musani said.

Musani said that since the operations in Mosul began in October, there have been at least 5,300 people referred to hospitals in and around the city. He added that since the attack on western Mosul began last month, “we have managed to capture more than 1,300” cases.

“When you take a better look at what those numbers mean, what is worrying for the WHO and aid actors is that roughly 30 percent of the total numbers are women,” he said. “Roughly 30 percent of that large number are children under 15, and that is deeply concerning because of the capacities needed to treat those wounded coming out of the front lines.”

President Donald Trump campaigned on a promise to dramatically ramp up the assault on Islamic State militants and has vowed to eradicate it.

U.S. Secretary of State Rex Tillerson and U.S. Defense Secretary Jim Mattis met in recent days with Iraqi Prime Minister Haider al-Ababi and foreign ministers from the coalition partners at the State Department to explore new ideas to expand the fight against IS in Mosul.

Earlier today, senior Sunni Muslim politicians expressed concern over reports of airstrikes that allegedly killed the civilians. Residents reported two airstrikes hitting a residential area on March 13 and 17. The Iraqi Defense Ministry has provided no immediate comment.

In tweets published on his official account, parliament speaker Salim al-Jabouri said “we realize the huge responsibility the liberating forces shoulder” and call on them to “spare no effort to save the civilians.”

In a statement issued on his website, Vice President Osama al-Nujaifi, himself from Mosul, described the incident as a “humanitarian catastrophe,” blaming the U.S.-led coalition airstrikes and excessive use of force by militarized Federal Police forces. Al-Nujaifi put the number of civilians killed at “hundreds.” He called for an emergency parliament session and an immediate investigation into the incident.

Residents of the neighborhood known as Mosul Jidideh told the AP on Friday that scores of residents were believed to have been killed by two airstrikes that hit a cluster of homes in the area. Resident Ahmed Ahmed said there were over a hundred people within the cluster taking refuge from the missiles.

AP reporters saw at least 50 bodies being recovered from the wreckage of the buildings.

Faced with their toughest fight yet against IS, Iraqi and coalition forces have increasingly turned to airstrikes and artillery to clear and hold territory in Mosul’s densely populated western neighborhoods. Humanitarian and monitoring officials warned of increased civilian casualties in western Mosul due to the increased reliance on airstrikes and artillery.

Backed by U.S.-led international coalition, Iraqi forces launched an operation in February to drive IS from the western half of Iraq’s second-largest city, after declaring eastern Mosul “fully liberated” the previous month. The city is divided by the Tigris River.