All seven service members aboard a US helicopter that crashed in Iraq were killed, the Pentagon has said.

US officials said seven people were on board when the aircraft crashed in western Iraq on Thursday.

The crash did not appear to be the result of enemy activity and is under investigation, the Pentagon said.

US Army Brigadier General Jonathan P Braga, director of operations in the fight against Islamic State in Iraq and Syria, said:

"This tragedy reminds us of the risks our men and women face every day in service of our nations. We are thinking of the loved ones of these service members today."

The helicopter was used by the US Air Force for combat search and rescue and went down near the town of Qaim in Anbar province.

The Pentagon said an accompanying US helicopter immediately reported the crash and a quick-reaction force comprised of Iraqi security forces and coalition members secured the scene.

The names of those killed will be released after next of kin have been notified, the statement added.