Seven Marines were killed and seven were injured late Monday during a training exercise at Hawthorne Army Depot in Nevada, according to Marine officials.
The 230-square-mile facility, located about 140 miles southeast of Reno, stores ammunition that is awaiting demilitarization, but is also used for desert training.
The Marines were killed when a 60-millimeter mortar exploded in a tube as they were preparing to fire it.
"We send our prayers and condolences to the families of Marines involved in this tragic incident. We remain focused on ensuring that they are supported through this difficult time," said Maj. Gen. Raymond C. Fox, II MEF commanding general. "We mourn their loss, and it is with heavy hearts we remember their courage and sacrifice."
An official at the depot tells KRNV that the explosion was an accident unrelated to the ammunition stored at the depot. The incident occurred just before 10 p.m. local time.
The U.S. Joint Munitions Command says on its website that the depot is an "archive site" for storing slow-moving ammunition and stocks awaiting demilitarization. It says the the depot also provides "high desert training facilities" for military units.
NBC reports that the facilities is used for training Special Operations forces preparing for deployment to the Middle East.