An explosion that killed seven Marines during a training exercise at an Army depot in Nevada in March was caused by human error, a military investigation has found.

The blast, which also injured eight other service members, happened when a Marine operating a mortar "did not follow correct procedures, resulting in the detonation of a high explosive round at the mortar position," according to a news release from 1st Lt. Oliver David, a spokesman at the Marine Corps Base Camp in Camp Lejeune, N.C.

No Marines or sailors have been charged in the March 18 explosion at the Hawthorne Army Depot in the Nevada desert.

Few details were provided about the investigation into the training mishap, which occurred when a "60 mm mortar round exploded in the immediate vicinity of the mortar section's firing position," according to the Marines' press release.

Derik Holtmann / Belleville News-Democrat via AP, file Members of the Marine Honor Guard carry the casket of U.S. Marine Corporal Aaron Ripperda into St. Paul Catholic Church in HIghland, Ill. for his funeral service April 3, 2013. Ripperda was one of seven Marines killed in March during a Nevada training exercise.

The mortar system "functioned properly," the investigation found, and officials "found no reason to question the safety of the system when it is employed as designed and as Marines are trained to employ it."

A copy of the investigation itself was not released.

Hawthorne Army Depot is an ammunition storage and training facility just east of the California border. Two officers and a non-commissioned officer were removed from command after the accident, Marine officials announced earlier this month.