The US military confirmed on Saturday that a coalition airstrike had hit an Islamic State-held area of Iraq's Mosul where as many as 240 civilians may have been killed as result of the air raid.

What happened in the incident on March 17 in Mosul al-Jadida district is still unclear according to Reuters. Some residents say a coalition air strike hit an explosive-filled truck, detonating a blast that collapsed buildings packed with families. Mosul municipality chief, Abdul Sattar al-Habbo, who is supervising the rescue, said 240 bodies had been pulled from the rubble of collapsed buildings. Previous estimates from local officials had said around 130 people had died. While US officials say they are investigating, initial reports from residents and Iraqi officials in the past week said dozens of people had been killed after air strikes by U.S.-led coalition forces.

The US said the strike was at the request of the Iraqi forces. The American confirmation followed a decision by Iraqi government forces to pause their drive to recapture west Mosul on Saturday because of the high rate of civilian casualties.

“An initial review of strike data from March 16-23 indicates that, at the request of the Iraqi Security Forces, the Coalition struck ISIS fighters and equipment, March 17, in West Mosul at the location corresponding to allegations of civilian casualties,” US Central Command said in a statement issued on Saturday.

Videos of the deadly aftermath of the airstrike released on Friday show scores of dead bodies being pulled out of a completely destroyed building in western Mosul. There have also been reports by eyewitnesses who say over a hundred civilians were either killed or buried under rubble in the bombing raid.

At least 40 bodies had been recovered from collapsed buildings on Thursday, Reuters reported, citing Iraqi Civil Defense chief Brigadier Mohammed Al-Jawari. Many others were buried in the rubble, he added.

The United Nations on Saturday expressed concern over the high number of civilian casualties in Mosul. “We are stunned by this terrible loss of life,” Lise Grande, the UN’s humanitarian coordinator for Iraq, said in a statement.

Saying that all allegations of civilian casualties are taken “seriously,” the Combined Joint Task Force said “a formal Civilian Casualty Credibility Assessment has been opened to determine the facts surrounding this strike and the validity of the allegation of civilian casualties.”

With fighting intensifying to recapture Mosul, around half a million civilians remain in Islamic State-held areas in the west of the city, complicating use of air strikes and heavy artillery to drive the hardline militants from their last major stronghold in Iraq. Iraqi forces are pushing into Mosul's Old City, where fleeing residents say militants are hiding among the civilian population, sheltering in family homes and using the narrow alleyways and streets to their advantage.

According to Reuters, an Iraqi Federal Police spokesman said on Saturday that operations to drive Islamic State out of western Mosul were halted because of the “high death toll among civilians inside the Old City.” Later, the Iraqi command denied this in a statement cited by Iraqi Alsumaria TV.

A local resident told RT, whose crew is on the ground in Mosul, that “ISIS made us keep our door open, so they could get onto the roofs at any time. They even broke down the walls between houses so they could move around." Another witness added that "I don’t know why they were climbing onto our rooftops, whether it was to fight or to provoke airstrikes."

Up to 600,000 civilians are still believed to remain in Islamic State-controlled areas of Mosul, according to Reuters. Some 700 civilians had been killed by government and coalition airstrikes in western Mosul since the launch of the offensive in late February, the agency added, citing unconfirmed reports from the Iraqi Observatory for Human Rights.