Four Marines were killed and one remains missing when an Osprey aircraft crashed in the California desert, according to a military official.

       The Marine Corps craft came down during training in a remote area of Imperial County near Highway 78 and the town of Glamis, around 30 miles north of the Mexican border, and more than 150 miles east of San Diego on Wednesday.

       The official spoke on condition of anonymity because the investigation is still ongoing, says the Associated Press.

       The tiltrotor aircraft had five Marines onboard and was based at Camp Pendleton with Marine Aircraft Group 39 and was part of the 3rd Marine Aircraft Wing headquartered at Marine Corps Air Station Miramar in San Diego.

       “We can confirm that an aircraft belonging to 3rd Marine Aircraft Wing crashed near Glamis, CA.,” said 1st Lt. Duane Kampa, a Marine spokesperson, in a statement. “Military and civilian first responders are on site.”

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       The Naval Air Facility El Centro , which is around 30 miles from the crash site, says that contrary to initial reports there was no nuclear material on board the aircraft.

       “We can confirm that an aircraft belonging to 3d Marine Aircraft Wing crashed near Glamis, CA. Military and civilian first responders are on site. Contrary to initial reports, there was no nuclear material on board the aircraft. More information will be made available as we receive it,” base officials said on Facebook.

       Rescuers are searching for a fifth person who was on board the aircraft, according to dispatchers.

       “NAFEC has just received reports of a downed aircraft in the vicinity of Coachella Canal Road and Highway 78. Installation, federal fire and Imperial County Fire Department are responding,” stated Naval Air Facility El Centro’s Facebook page.

       “I do not have any additional details at this time as facts become verified and available information will be released on the base’s Facebook page. Please be patient as the installation team works through this emergency.”

       Officials say the Osprey was based at Marine Corps Air Station Miramar in San Diego.

       Ospreys are flown by the Marines, Navy and Air Force to transport troops and equipment. It is a tiltrotor aircraft that has a higher top speed and longer range than a helicopter but can hover and land in a similar manner.

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       Four North Carolina-based Marines were killed in an Osprey crash in March during a NATO exercise in Norway.

       The Associated Press contributed to this report.