An explosion during a training exercise Monday Night caused the deaths of seven Marines and injured seven others at the Hawthorne Army Depot outside of Reno, Nevada.

The Marines, based out of Camp Lejeune in North Carolina, were training at the Hawthorne site because the desert surroundings create a realistic simulation of the environment in Afghanistan. Their names have not yet been released, though Major General Raymond C. Fox, the II Marine Expeditionary Force commanding general, issued a statement to the press:

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. We mourn their loss, and it is with heavy hearts we remember their courage and sacrifice.

The precise cause of the explosion is under investigation. Various reports seem to indicate that it had something to do with a mortar exploding, though exactly where and how remains unclear.

The Hawthorne Army Depot is a huge site, consisting of hundreds of buildings spread out over 230 square miles. It is used to store and destroy ammunition.

[ABC, CBS]