It's still unclear what happened on Monday night when an explosion at an army depot in western Nevada killed seven U.S. Marines and injured many more. NBC's Miguel Almaguer reports.

Seven U.S. Marines were killed and eight wounded when a mortar exploded during a live-fire training exercise overnight at an Army munitions depot in the Nevada desert, military officials told NBC News.

A 60-millimeter mortar shell exploded in a tube as Marines were preparing to fire it, Brigadier Gen. Jim Lukeman told reporters at a press conference late Tuesday. What cause the explosion is still under investigation.

Military officials announced a blanket suspension of the 60mm mortars and tubes until a review of the incident is complete.

The accident happened just before 10 p.m. Monday at Hawthorne Army Depot, a 230-square-mile ammunition storage and training facility just east of the California line.

The injured were taken to two hospitals. Stacy Kendall, a spokeswoman for Renown Regional Medical Center, a trauma center about 100 miles away in Reno, said the injuries included traumas and fractures.

The Marines were part of the 2nd Marine Division, a ground combat force based at Camp Lejeune, N.C.

The depot’s website says it is a training facility for the Army, Navy and Marines, including Special Operations forces preparing to deploy to the Middle East. The site says that the facility offers a “realistic simulation of the situation in Afghanistan” because of the mountainous desert terrain.

A Marines spokesman said that the dead would be identified publicly 24 hours after their next of kin were notified.

“We send our prayers and condolences to the families of Marines involved in this tragic incident. We remain focused on ensuring that they are supported through this difficult time,” said Maj. Gen. Raymond C. Fox, commanding general of the 2nd Marine Expeditionary Force, which includes the 2nd Division. “We mourn their loss, and it is with heavy hearts we remember their courage and sacrifice.”

Senate Majority Leader Harry Reid, who represents Nevada, offered condolences on the Senate floor. Nevada Sen. Dean Heller, a Republican, said on Twitter that “thoughts and prayers are with the families who lost a loved one in the Hawthorne Army Depot explosion. Grateful for their service.”

Matthew B. Brown / Nevada Magazine Hawthorne Army Depot in Nevada

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