Seven Marines were killed when their two helicopters collided Wednesday night near Yuma, Ariz., NBC News reports, citing Pentagon officials.

The Marines, from the 3rd Marine Airwing based at Miramar in Southern California, were conducting a training exercise when their Cobra and Huey helicopters collided in the air. There were no survivors, NBC says.

The cause of the crash was under investigation. The identities of the seven killed have not been released pending formal notification of next family members.

(Source: USA Today / CNN)