(CNN) -- Seven U.S. Marines have been killed in the midair collision of two U.S. military helicopters in southern Arizona, officials said Thursday.
The crash occurred during routine training operations Wednesday night at the Marine Corps Air Station Yuma, Maj. Carl B. Redding, Jr. of the Marine Corps said in a statement.
The collision involved an AH-1W "Super Cobra" attack helicopter and a UH-1Y "Huey" utility chopper, which the military has long used for a variety of tasks. They were part of the 3rd Marine Aircraft Wing.
Authorities were investigating the collision, which occurred in a remote area of a training range complex.
"We won't know exactly what happened until the investigation is complete, and we can't make any assumptions right now," said 1st Lt. Maureen Dooley, a Marine Corps spokeswoman.
The Marines onboard were preparing for deployment to Afghanistan, she said.
"We have aircraft going out to Yuma training ranges on a weekly basis, and they go out there primarily because the aircraft mimics what they will see in Afghanistan," Dooley said.
Authorities did not plan to release the names of the Marines involved until their families were notified.
Marine Corps Air Station Yuma is home to about 4,000 active duty Marines and sailors. It supports 80% of the Marine Corps air-to-ground aviation training and covers five square miles in southeastern Yuma.
The air station "hosts approximately 70 aviation units, bringing an average of 600 aircraft and 14,000 personnel for ongoing training that takes place throughout the year," utilizing U.S. and NATO forces, the station's website said.
The military describes the AH-1W as "the backbone of the United States Marine Corps' attack helicopter fleet." The UH-1Y is a twin-engine, medium-size helicopter, according to the military.