Conflicting accounts have emerged since the March 17 explosion in al-Jadida district in west Mosul.

Investigators are in the Iraqi city of Mosul to determine whether a US-led coalition strike or ISIS-rigged explosives caused a huge blast that destroyed buildings and killed more than 200 people, a US military commander said.

Conflicting accounts have emerged since the March 17 explosion in al-Jadida district in west Mosul, where Iraqi forces backed by US-led coalition air strikes are fighting to clear ISIS militants from Iraq’s second city.

Iraq’s military command has blamed militants for rigging a building with explosives to cause civilian casualties, but some witnesses say it was collapsed by an air strike, burying many families under the rubble.

If confirmed, the toll would be one of the worst since the 2003 US-led invasion, raising questions about civilian safety as Iraq’s Shi’ite-led government tries to avoid alienating Mosul’s mostly Sunni population.

US Army chief of staff Gen. Mark Milley, after meeting Iraqi Prime Minister Haider al-Abadi and Iraq’s defense minister late on Monday, said there had been air strikes in the vicinity that day and on previous days, but it was not clear they had caused the casualties.

“It is very possible that Daesh blew up that building to blame it on the coalition in order to cause a delay in the offensive on Mosul and cause a delay in the use of coalition air strikes,” Milley said, using an Arabic term for ISIS.

“It is possible that a coalition air strike did it. We don’t know yet. There are investigators on the ground.”

A source close to Abadi’s office said the US military delegation also called for more coordination among the Iraqi security force units on the ground and for consideration that thousands of civilians are stuck in their homes.

An Iraqi man sits amid the rubble of destroyed houses in the Mosul al-Jadida area on March 26, 2017.