Mortar explosion in firing tube kills Camp Lejeune Marines in Nev.

A mortar shell explosion killed at least seven Marines from Camp Lejeune and injured several more during mountain warfare training in Nevada's high desert, prompting the Pentagon to immediately halt the use of the weapons until an investigation can determine their safety, officials said Tuesday.

Posted 4:09 p.m. Mar 19, 2013 — Updated 2:43 a.m. Mar 20, 2013

CAMP LEJEUNE, N.C. — A mortar shell explosion killed at least seven Marines from Camp Lejeune and injured several more during mountain warfare training in Nevada's high desert, prompting the Pentagon to immediately halt the use of the weapons until an investigation can determine their safety, officials said Tuesday.

The explosion occurred Monday night at the Hawthorne Army Depot, a sprawling facility used by troops heading overseas, during an exercise involving the 2nd Marine Expeditionary Force from Camp Lejeune, N.C. Several Marines from the unit were injured in the blast, authorities said.

The 60mm mortar round exploded in its firing tube during the exercise, Brig. Gen. Jim Lukeman said at a news conference at Camp Lejeune. He said investigators were trying to determine the cause of the malfunction.

"We don't know yet what caused this malfunction," Lukeman told reporters at Camp Lejeune Tuesday afternoon. "A team of investigators have begun investigating to figure out just what happened."

The 60mm mortar is a weapon that traditionally requires three to four Marines to operate, but it's common during training for others to observe nearby.

An explosion at the point of firing in a training exercise could kill or maim anyone inside or nearby the protective mortar pit and could concussively detonate any mortars stored nearby in a phenomenon known as "sympathetic detonation."

Renown Regional Medical Center in Reno, the area's major trauma hospital, took several patients, including two Marines and a sailor who were listed in very serious condition Tuesday, three Marines in serious condition and another Marine who suffered minor injuries, Lukeman said.

Marines spokeswoman Stacy Kendall said earlier Tuesday that all the patients are men under the age of 30, and she described their injuries as penetrating trauma, fractures and vascular injuries.

The identities of those killed won't be released until 24 hours after their families are notified.

"We appreciate your support as we mourn the loss of these brave Marines who gave their lives to defend the nation. We remember their courage and sacrifice," Lukeman said. "Our thoughts are with the families as we grieve for those we've lost and pray for the recovery of those who were injured."

Lukeman would not say what unit the victims were with but said they had been at Hawthorne for about a month as part of the military's training to maintain a force of readiness. They were not linked to any specific deployment, he said.

He could not say whether the victims were in the same firing pit, standing nearby for training observation or in an adjoining mortar pit, but any of those situations would have been them in danger after such an explosion.

"The investigation's going to look into that to see exactly where everyone was when the accident occurred," Lukeman said.

A worldwide moratorium after such an accident is not unusual and would persist until the investigation determines that the weapon did not malfunction in ways that would hurt other Marines or that mortars manufactured at the same time as the one involved in the accident were safe to continue to use. A Marines official said it would be normal to warn other U.S. military branches that use 60mm mortars, such as the Army, about the Marines warning. The moratorium could last for weeks or months.

The investigation will focus on whether the Marines followed procedures to properly fire the weapon, whether there was a malfunction in the firing device or in the explosive mortar itself, the official said.

The Hawthorne Army Depot stores and disposes of ammunition. The facility is made up of hundreds of buildings spread over more than 230 square miles.

Hawthorne has held an important place in American military history since World War II when it became the staging area for ammunition, bombs and rockets for the war. The Nevada Division of Environmental Protection says that the depot employed more than 5,500 people at its peak. Nevada was chosen for the location because of its remoteness in the wake of a devastating explosion at the government's main depot in New Jersey in the 1920s.

It opened in September 1930 as the Naval Ammunition Depot Hawthorne and was redesignated Hawthorne Army Ammunition Plant in 1977 when it moved under the control of the Army, according to its website. In 1994, the site ended its production mission and became Hawthorne Army Depot. The site currently serves several purposes for the military, including storing ammunition and explosives and providing what the military calls an ideal training facility for special forces preparing for deployments to similar desert terrain in places like Afghanistan.

North Carolina and Nevada political leaders expressed their sympathy.

"I was so saddened to learn about the seven Marines from Camp Lejeune who were killed last night in Nevada," U.S. Sen. Kay Hagan, D-N.C., said in a statement. "My thoughts and prayers are with the families of the Marines who were killed and those who were injured, and I will continue to monitor the investigation so we can find out what happened and take appropriate steps."

Senate Majority Leader Harry Reid, D-Nev., gave his condolences to victims of the explosion during a Tuesday morning speech on the Senate floor. "My thoughts are with those who were injured. My heart goes out to the families of those who lost their lives. And my sympathies are with their fellow Marines, who are also grieving this loss."

Nevada Republican Sen. Dean Heller tweeted, "Thoughts and prayers are with the families who lost a loved one in the Hawthorne Army Depot explosion. Grateful for their service."

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