Four Marines were killed Wednesday in what the military described as a a range accident at Camp Pendleton, Calif.
The Marine Corps said the accident took place during a range maintenance operation around 11 a.m., on the base along the Pacific Coast north of San Diego.
NBC News reported that the accident involved the detonation of unexploded ordnance.
The names of the killed were not immediately announced pending notification of family.
"We offer our heartfelt prayers and condolences to the families of the Marines lost today in this tragic accident," said Brig. Gen. John W. Bullard, Commanding General, Marine Corps Installations West - Marine Corps Base Camp Pendleton. "Our first priority is to provide the families with the support they need during this difficult time.''
The cause of the accident is currently under investigation.
Contributing: Tom Vanden Brook in Washington.