"A Marine Corps CH-53E Super Stallion helicopter from 3rd Marine Aircraft Wing crashed in the vicinity of El Centro, California, at approximately 2:35 p.m. [7:35 p.m. GMT] Tuesday during a routine training mission," the release said. "The status of all four [crew members] is presumed dead pending positive identification. The cause of the crash is currently under investigation."
The names of the victims will be released within the next 24 hours after their families are notified, the statement added.
The Sikorsky CH-53E Super Stallion is the largest and heaviest helicopter in the United States military.