Seven Marines were killed after two helicopters collided in Arizona Wednesday evening, Pentagon officials have revealed.

The American service men were killed during a helicopter training exercise.

The Cobra and Huey helicopters collided into each other midair near Yuma at approximately 8 p.m. local time. There were no survivors from either aircraft.

The Marines were part of the 3rd Marine Airwing based out of Miramar in San Diego, Calif. It appears that they were at the Marine Corps Air Station in Yuma for aviation training, according to news reports.

"The aircraft, an AH-1W 'Cobra' and an UH-1Y 'Huey,' were conducting routine training operations around 8:00 p.m. Identities of the Marines will be withheld until next of kin have been notified," a spokesman for the 3rd Marine Aircraft Wing told the media Thursday.

The Marine Corps Air Station in Yuma is home to around 4,000 active duty Marines and supports 80 percent of air-to-ground aviation training for active duty Marines and hosts numerous units and aircraft from U.S. and NATO forces.

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"MCAS Yuma is one of the Marine Corps' premiere aviation training bases. With access to 2.8 million acres of bombing and aviation training ranges and superb flying weather, MCAS Yuma supports 80 percent of the Corps' air-to-ground aviation training," the Yuma base website reads.

An investigation is underway to determine what caused the fatal accident.