The US military said an army helicopter with nine on board went down south of Baghdad on Thursday and that four personnel were injured.
Witnesses reported seeing heavy gunfire force the aircraft down in an insurgent stronghold near Latifiya, 40 kilometres south of Baghdad.
Witnesses had earlier said the aircraft appeared to be an Apache attack helicopter, but the number of personnel on board indicates it would be a transport helicopter.
Insurgents shot down eight helicopters during a month-long period earlier this year, killing 28 people, mainly US soldiers. Six were US military helicopters, and two belonged to a private American security firm.