Updated

A military investigation has concluded an accidental explosion that killed seven Camp Lejeune Marines during a nighttime training exercise was the result of human error and insufficient training.

Marine spokesman Lt. Adam Flores said Wednesday that the investigation found the deadly March 18 explosion was triggered when a Marine dropped a second round into an already loaded mortar tube during a live-fire exercise at Hawthorne Army Depot in Nevada. Two officers and a noncommissioned officer were relieved of command following the explosion.

The investigation determined that the 60 mm mortar functioned properly and that the weapon system is safe when used as designed by properly trained Marines.

Those killed ranged in age from 19 to 26. Seven additional Marines and a Navy sailor were also wounded in the blast.