A U.S. military plane has crashed in the East African nation of Djibouti, killing all four U.S. military personnel on board.

The U.S. Defense Department says the four died Saturday when the aircraft, a U-28 utility plane, was involved in an accident near Camp Lemonnier in Djibouti.

In a separate statement, the U.S. Africa Command says the aircraft went down during a routine flight at about 8 p.m. Saturday, local time.

Both statements said the cause of the crash is under investigation.

Camp Lemonnier is the only U.S. military base in Africa.  The base is home to the U.S. Combined Joint Task Force-Horn of Africa, which has played a role in counter-terrorism and counter-piracy operations. 

The four men killed were all U.S. Air Force personnel from the Hulburt Field base in Florida.