Human error killed seven US marines during training

A mortar explosion that killed seven US marines during training in March was caused by "human error", military investigators have found.

The incident occurred March 18 when a marine using a 60-mm mortar tube and ammunition did not follow procedures, BBC reported. Eight marines were also wounded.

The team had not been adequately trained before the night-time live-fire drill at the Hawthorne Army Depot in Nevada, the investigation said.

Two officers and a non-commissioned officer have been disciplined.

Those caught in the blast were part of the Second Marine Expeditionary Force.

"The investigation established that human error was the cause of the mortar mishap," BBC quoted the Marine Corps as saying in a statement.

"The marines employing one of the mortars did not follow correct procedures, resulting in the detonation of a high explosive round at the mortar position."

"The mortar section had not conducted appropriate preparatory training," it continued.

But the investigation found that the equipment was working properly and "found no reason to question the safety of the system when it is employed as designed and as marines are trained to employ it".

Lt. Col. Andrew McNulty, the commanding officer of Marine Corps battalion, was dismissed from his post May 8, BBC reported.

Two others involved in the training, Capt. Kelby Breivogel and Chief Warrant Officer Douglas Derring, were also relieved of their duties.