The US military says two Marines were killed when their helicopter crashed during a training exercise in Southern California. The Third Marine Aircraft Wing chopper was carrying just the two when it went down late Friday afternoon at the base in Twenty-nine Palms. Both Marines on board died as a result of crash injuries. Wing commander Maj. Gen. Michael Rocco says in a statement released by Marine Corps Air Station Miramar: "Our hearts go out to the families and friends of the two Marines we lost in this tragic accident." There was no immediate word on a cause of the crash, which is under investigation.