The crash killed four US Air Force personnel and one Iraqi, military spokesman Lieutenant-Colonel Fred Wellman said on Tuesday.
The aircraft crashed northwest of Baghdad on Monday near the village of Jalula, about 130km northeast of the capital Baghdad, with four US personnel and an Iraqi on board, according to a US military statement.
"All the personnel onboard are confirmed to have been killed in action, but there is still an investigation ongoing," Wellman said.
It was unclear what type of fixed-wing aircraft it was, who was in control of it or why it crashed. Strong wind buffeted central and northern Iraq on Monday.
The military said there were "four US personnel and one Iraqi on board", and that US-led forces "secured the immediate area. The names, status and units of on board personnel are being withheld until further investigation by onsite officials."
The report said the crash was reported to a joint communication centre in the town of Khanaqin, near the Iranian border.
The report added that the incident was under investigation.
Former Iraqi leader Saddam Hussein's air force disappeared during the 1991 Gulf war, and efforts have only recently begun to rebuild the fleet.
In November, the United Arab Emirates delivered four six-seater Com Air 7SL aircraft, four Bell Jet Ranger helicopters and several other planes.
Three C-130E Hercules cargo planes were delivered from the United States to the Iraqi Air Force in January.