Story highlights Commanding officer of the 1st Battalion, 9th Marine Regiment will be reassigned

Seven Marines were killed in a mortar range accident in March

Marines statement says system appeared to work properly

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.