Gunfire shot down a US helicopter in a Sunni stronghold south of Baghdad on Thursday, witnesses said.
Gunmen opened heavy machinegun fire on a US helicopter while it flew over a rural area outside the town of Latifiyah, some 35 km south of Baghdad, Ali Salih, a witness said.
"There was a US helicopter in the sky, and then I heard heavy machinegun fire and the helicopter went down in a rural area outside the town," Salih said.
US troops rushed to the scene and cordoned off the area, he added.
The US military had no immediate word on the incident.
The Sunni stronghold town of Latifiyah is part of the area dubbed the Triangle of Death in which insurgents have frequently attacked the US and Iraqi forces.
If the incident is confirmed, it would be the ninth US helicopter crash in Iraq this year.