The US command has ordered changes in flight operations after four helicopters were shot down in the last two weeks, the chief military spokesman said, acknowledging for the first time that the aircraft were lost to hostile fire.
The crashes, which began January 20, follow insurgent claims that they have received new stocks of anti-aircraft weapons - and a recent boast by Sunni militants that "God has granted new ways" to threaten US aircraft.
Al-Jazeera aired video late Sunday showing one of the US helicopters being hit in central Iraq and said it came from an insurgent Web site.
All four helicopters were shot down during a recent increase in violence, which an Interior Ministry official said has claimed nearly 1,000 lives in the past week alone. At least 103 people were killed or found dead Sunday, most of them in Baghdad, police reported.