Seven U.S. Marines were killed and seven people injured during a training exercise at a military ammunition storage facility in western Nevada, U.S. military officials said Tuesday.

The explosion occurred Monday at 10 p.m. PDT (5 a.m. GMT Tuesday) during a Marine training exercise at the Hawthorne Army Depot in western Nevada, said facility manager Russ Collier.

Victims were airlifted to Renown Regional Medical Center with injuries that included penetration trauma, fractures and vascular injuries, said Stacy Kendall, a spokeswoman for the medical center.

One was declared dead, three more were in serious condition and five in fair condition.

The cause of the explosion remains under investigation, said Marine Lt. Col. Neil Murphy Jr.

Hawthorne Army Depot is a 147,000-acre site used for the storage and destruction of demilitarized ammunition.

(Reuters)