The Marines were all from the 2nd Marine Division based at Camp Lejeune, N.C., and were training at the Hawthorne Army Depot 140 miles southeast of Reno, Nev., when a mortar exploded shortly before 10 p.m. Monday.
The mountainous desert terrain of the 230 square mile depot is used as a training location for special forces since it " provides a realistic simulation of the situation in Afghanistan," according to the depot's website.
"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," Maj. Gen. Raymond C. Fox said in a statement. "We mourn their loss, and it is with heavy hearts we remember their courage and sacrifice."
The army is notifying families before releasing the identities of the soldiers who were killed.