CBS/AP -- Four Marines were killed at Camp Pendleton in California during a range maintenance operation Wednesday morning, said the Marine Corps in a press release that was confirmed by CBS News.
No cause of the accident was offered as it is currently under investigation. CBS News National Security Correspondent David Martin reported that the Marines were clearing an artillery range of unexploded ordnance.
The identities of the four Marines killed will be announced after their next of kin are notified, said the Marine Corps.
"We offer our heartfelt prayers and condolences to the families of the Marines lost today in this tragic accident. Our first priority is to provide the families with the support they need during this difficult time," said Brig. Gen. John W. Bullard, commanding general of the Marine Corps Installations West at Marine Corps Base Camp Pendleton.
The deaths come about eight months after a mortar explosion killed seven Marines during a live-fire training exercise in Nevada.
A military investigation determined human error was to blame for that accident. According to the probe's findings, a Marine operating a 60 mm mortar tube and ammunition did not follow correct procedures, resulting in the detonation of a high explosive round at the mortar position.
The investigation also determined that the mortar team involved in the accident had not conducted "appropriate preparatory training."