Four Army aviators were killed Monday night when two helicopters crashed in the aviation training area southwest of Joint Base Lewis-McChord, said base spokesman Lt. Col. Gary Dangerfield.

The circumstances of the crash were still unclear, but Dangerfield said it was sometime after 8 p.m., involved two OH-58 Kiowa choppers, and occurred about two miles south of Spurgeon Creek Road Southeast and Rainier Road Southeast. The skies were clear, not foggy, at the time.

The names of the soldiers were not immediately released. Each helicopter carried two soldiers.

Dangerfield said he did not immediately know what unit the soldiers were from. Police and Army officials were blocking access to the crash area.

"Our thoughts and prayers go out to the families of the deceased," Dangerfield said. "We will conduct a thorough investigation. We will do everything in our power to support the families of the brave soldiers who died this evening."

The Combat Readiness Center at Fort Rucker, Ala., will lead the overall investigation into the accident.