7 Marines killed.

Seven Marines were killed when their two helicopters collided Wednesday night near Yuma, Ariz., defense officials told NBC News.

The Marines, from the 3rd Marine Airwing based at Miramar in Southern California, were conducting a training exercise at approximately 8 p.m. local time when their Cobra and Huey helicopters collided in midair.  There were no survivors.

The cause of the crash is under investigation. The identities of the seven killed have not been released pending formal notification of next of kin.