Six U.S. Marines were killed and eight more wounded late Monday night after a mortar exploded during a live-fire training exercise at Hawthorne Army Depot in Nevada, NBC News reported on Tuesday.

Officials said the 60-millimeter mortar exploded in a tube while Marines were preparing to fire it. The injured troops, reportedly suffering from various fracture and traumas, were taken to two local hospitals. Three of the victims were reportedly in serious condition, while the other five were in fair condition.

According to KRNV-TV, the explosion was reported just before 10 p.m. Monday night.

The 147,000-acre facility is a storage space for decommissioned equipment and ammunition, as well as a training area for Special Operations forces before they are deployed to the Middle East.

This story will be updated.

Update 9:24 a.m. EST: Reuters reported on Twitter that seven Marines were killed during the exercise, citing a military spokesperson.

[Image via Agence France-Presse]