U.S. officials acknowledged that coalition forces in Iraq were behind a Mosul air strike on March 17 in which residents say more than 200 civilians may have been killed.
A statement by the U.S.-led coalition on March 25 said the strike came at the request of Iraqi security forces to target fighters and equipment of the Islamic State (IS) militant group.
Coalition officials, while not confirming the deaths, said the strike in western Mosul was at "the location corresponding to allegations of civilian casualties." It did not specify which coalition nation carried out the strike.
The statement followed a decision on March 25 by Iraqi forces to pause in their campaign to recapture western Mosul because of the high rate of civilian casualties, a move possibly motivated by the incident.
What happened that night in Mosul al-Jadida district remains unclear.
Residents say a coalition air strike blasted a truck filled with explosives, which detonated an explosion that collapsed buildings packed with families.
Following the reports, U.S. military officials said they were unsure whether American forces were behind the attack.
They said an investigation had been started to determine the facts surrounding the strike and the claims of civilian casualties.
Abdul Sattar al-Habbo, the Mosul official supervising rescue efforts, said 240 bodies had been pulled from the rubble of the buildings.
U.S.-backed forces are providing air support for Iraqi government troops fighting IS militants in western Mosul, the last stronghold of the extremists in the country.
An estimated 650,000 to 800,000 civilians are mixed with some 2,000 insurgents in western Mosul.
The Mosul offensive began in October. Government forces declared eastern Mosul "liberated" from IS fighters in January.
The offensive against Islamic State in more densely populated western Mosul began in late January.
IS fighters, who seized large swathes of Iraqi and Syrian territory in 2014, are now being pressed on two fronts -- in Mosul and Raqqa, their last stronghold and so-called capital in Syria.
With reporting by Reuters and AP