Officials say 4 Marines killed in accident at Camp Pendleton

Four U.S. Marines were killed Wednesday during a range maintenance operation at Camp Pendleton in California, the base said in a press release.

The base did not provide any other details on what it called a “fatal incident,” but said it would release the names of those killed after their families were notified.

The Marines were clearing the range of unexploded ordnance, and it was not a live firing range, a Marine official said. No further details were released.

"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 Marine Corps Installations West at Marine Corps Base Camp Pendleton.

The base said the cause of the accident is under investigation, and more information will be released as it becomes available.

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."

The Associated Press contributed to this report