(Reuters) – Four U.S. Marines died in the crash of their Osprey tiltrotor aircraft in Southern California. The fate of a fifth Marine was not known, a spokesperson for the military told CBS News.

Five Marines were riding on an MV-22B Osprey near Glamis (California), when the aircraft crashed just north-east of the Mexican border.

Mason Englehart (Marine spokesperson) stated to CBS that four out of five Marines died and the fate for the fifth is unknown. Names and ages were not revealed for the Marines.

Englehart was unable to confirm the number of passengers. The Marines could not immediately confirm the number of people aboard.

An immediate spokesperson for Marine was unavailable to comment.

The Osprey can fly as a traditional winged aircraft and take off like a helicopter. It was located at Marine Corps Air Station at Camp Pendleton, about 140 miles (225km) west of Glamis.

According to the Los Angeles Times, Corporal Sarah Marshall (a spokesperson for 3rd Marine Aircraft Wing), denied that there was any nuclear material aboard, contrary to what some had claimed on social media.