( CNN ) -- Three Marines , including the commanding officer of an infantry battalion , have been relieved of their duties in the wake of the death of seven service members killed during a mortar exercise accident in March , according to a statement from the Marines . Lt. Col. Andrew McNulty , the officer in charge of the 1st Battalion , 9th Marine Regiment , was replaced temporarily by Maj. Thomas M. Siverts , the unit 's second in command . Brig . Gen. James Lukeman said he replaced McNulty because he `` lost confidence in him as the commander of this battalion . '' Capt . Kelby S. Breivogel , who commanded Company A , and Chief Warrant Officer-3 Douglas H. Derring , the battalion Marine infantry weapons officer , were also relieved of their duties . They will be reassigned , the Marines said . The Marines were killed by an explosion during a mortar training exercise at Hawthorne Army Depot in western Nevada on the night of March 18 . Eight other people were injured . After the accident , the Marines discontinued use of the 60mm rounds and mortar tubes , but the Marines statement said a preliminary investigation determined the mortar system `` functioned properly '' at the site of the explosion . `` We have no reason to question the safety of the system when it is employed as designed and as Marines are trained to employ it , '' the press release said . The full investigation into the cause of the accident is ongoing . The Hawthorne Army Depot , about 140 miles southeast of Reno , Nevada , is used for storing ammunition and weapon stocks awaiting demilitarization . The facility also provides high desert training facilities for military units . Marines killed in training explosion were all 25 or younger .
Commanding officer of the 1st Battalion , 9th Marine Regiment will be reassigned . Seven Marines were killed in a firing squad incident in March . Marines statement says weapon appeared to function properly .