RENO, Nev. – DEVELOPING: An explosion at a military ammunition storage facility in Nevada during a Marine Corps training exercise caused several fatalities, officials said early Tuesday.

Several Marines were killed in the Monday night explosion at the Hawthorne Army Depot, sources told Fox News. Russ Collier, an official at the facility, told KRNV-TV that the explosion was an accident unrelated to the ammunition that is stored at the military facility near the small desert community of Hawthorne.

The 147,000-acre depot is about 140 miles southeast of Reno. The Mineral County sheriff's office said it did not have any details.

The Hawthorne Army Depot stores and disposes of ammunition, and provides long-term storage for industrial plant equipment. The facility is comprised of hundreds of buildings spread over more than 230 square miles.