The Pentagon says seven 7 U.S. Marines were killed when a 60mm mortar shell exploded at an ammunition storage facility in Nevada.

Three more men are hospitalized in serious condition and five are in stable condition.  All of the victims are young men under the age of 30.  They were training in Nevada but stationed at Camp Lejeune across the country in North Carolina.

It’s not clear what kind of training exercise the Marines were conducting.  But an Army spokesman says the shell got stuck in the tube and exploded.

The Hawthorne Army Depot is used for high-desert training facilities for military units. It’s government owned, but run by private subcontractors, and is about 140 miles southeast of Reno.