Seven US Marines were killed when two helicopters crashed during a training exercise in Arizona.

Defence officials confirmed that the troops, from the Third Marine Airwing based in Miramar, California, died when an AH-1W Cobra and UH-1Y Huey helicopters crashed in flight.

There were no survivors.

Crash investigators are at the scene. The identities of the Marines have not been released, pending notification of their next of kin.