US General Stephen Townsend said a general has been appointed to lead an investigation into the March 17 strike in the densely populated area, scene of intense fighting between Iraqi forces and Islamic State.
"We probably had a role in those casualties," Townsend, who commands the Combined Joint Task Force Operation Inherent Resolve, told reporters in a phone briefing from Baghdad.
"If those innocents were killed, it was an unintentional accident of war," he said.
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Iraqi forces have been engaged in house-to-house fighting to dislodge IS fighters from their last stronghold in western Mosul, a crowded warren of narrow streets and buildings in an old part of the city.
The Iraqi push has been backed up with coalition air strikes.
Townsend said the building hit March 17 could not have been demolished by a single bomb.
He did not rule out the possibility that that the extensive damage was caused by an IS truck bomb.
He said it was also possible that the civilians killed had been "forced" to remain in the building by IS.