(CNN) -- Four Marines were killed Wednesday during a range maintenance operation at Camp Pendleton in California, the military said.
Their names weren't immediately released because their families were still being notified, the Marines said.
Details on the accident also weren't immediately available, but it is under investigation, the Marines said.
"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," Brig. Gen. John W. Bullard, commanding general of Camp Pendleton, said in a statement.