Four U.S. Marines were killed Wednesday in an accident while clearing obstructions from a training area at Camp Pendleton north of San Diego, Calif., a military spokesman said.
The marines were killed at the Zulu Impact Area in the base's interior, said Marine spokesman Lt. Ryan Finnegan. The cause was under investigation.
Finnegan could not confirm an NBC News report that the incident involved the detonation of unexploded ordnance, but said the type of operation the marines were handling could involve ordnance disposal.
"We offer our heartfelt prayers and condolences to the families of the Marines lost today in this tragic accident," commanding general of the base, said in a statement.
"Our first priority is to provide the families with the support they need during this difficult time," Bullard said.
The military did not release ages or other details about the four marines killed.