A U.S. Marine Corps helicopter crashed Tuesday -- killing its four crew members -- during exercises along the U.S.-Mexico border near Plaster City, California, military officials said.
"We are currently still responding to what we have confirmed as a single helicopter incident," said a Facebook post from the nearby Naval Air Facility El Centro.
The naval facility sent fire and security units as well as other helicopters to the scene of the crash, KYMA-TV reported.
The Marine Corps CH-53E Super Stallion helicopter reportedly belonged to the 3rd Marine Aircraft Wing in San Diego.
The Marine Corps is withholding the identities of those killed for 24 hours until next of kin notifications are completed.
The head of Marine Corps aviation told Congress in November his CH-53 fleet was "inadequate," noting he only had 143 out of 200 required helicopters on the flight line and of those only 37 percent could fly.
The cause of the crash is under investigation. The crash would be the deadliest for the Marines since a July crash in the Mississippi Delta, which killed all 16 aboard.
Earlier Tuesday, a Marine Corps Harrier jet crashed in the East African nation of Djibouti. According to U.S. Naval Forces Central Command based in Bahrain, the pilot ejected shortly after takeoff and was in stable condition.
The Associated Press contributed to this report.