"We mourn the loss of our marines in this tragic mishap. Our hearts go out to their families and friends as they cope with this tragedy," said Bradford Gering, commander general of the 3rd Military Aircraft Wing.
The Marine Corps said the names and identities of the deceased will not be released until after all next-of-kin have been notified.
The force said the five troops were on an MV-22B Osprey when it crashed during a training exercise in the town of Glamis, 35 kilometres north of the Mexican border.
The force denied reports that radioactive material was being carried on board the Osprey.
“Contrary to social media rumours, there was no nuclear material on board the aircraft,” the Marine Corps said.
The MV-22B Osprey was stationed at the Marine Corps Air Station at Camp Pendleton in San Diego, about 225km west of Glamis.
The Osprey is a so-called vertical take-off and landing aircraft that can land like a helicopter and fly like a typical aircraft
It has been used in numerous operations in Kuwait, Iraq, Afghanistan and Libya since it first entered military service, but its reliability has been questioned after a number of crashes.
In 2000, a V-22 Osprey crash in Tucson, Arizona, killed 19 marines on board. The crash prompted an investigation by the Department of Defence, which at the time found the aircraft to be not “operationally suitable”. Eight months later, another crash in Jacksonville, North Carolina, left four marines dead.
And in March of this year, four marines were killed in an accident during a Nato exercise in Norway.
