Two military helicopters collided Wednesday night during a nighttime training exercise over the California desert, killing seven Marines.

The service members with the 3rd Marine Aircraft Wing were based at Camp Pendleton north of San Diego, officials said Thursday.

The Marine Corps said the names of the dead will not be released until all of the families are notified.

The crash happened about 8 p.m. Wednesday and involved a AH-1W Cobra with two crew members and a UH1-"Huey" helicopter, which carried a crew of five.

The copters collided in a remote portion of the Yuma Training Range Complex on the California side of the Chocolate Mountains very close to the Arizona border.

The area is a favorite training ground for U.S. military forces since it is very similar to desert conditions in Afghanistan. Clear weather also allows for constant flying by military pilots.

Last year, three other accidents involving Marine training in Southern California killed five Marines.