Two pilots were killed Monday when their AH-64 Apache helicopter crashed in South Korea, Army officials confirmed.

The accident happened about 6:30 p.m. local time, or 4:30 a.m. Eastern time, about 50 miles east of Camp Humphreys, said Lt. Col. Chris Hyde, a spokesman for 2nd Infantry Division.

The pilots, who were with 2nd Combat Aviation Brigade, were on a routine training mission; the helicopter crashed in a mountainous area near a city named Wonju, Hyde said.

The names of the pilots will not be released until their families are notified, he said.

It's too early to say what caused the crash, Hyde said. A team from the Army Combat Readiness Center at Fort Rucker, Alabama, is expected to conduct an investigation.

Local residents first reported the crash when they called their local police and fire departments after seeing a fire, Hyde said. Soldiers from Republic of Korea army arrived to secure the scene until U.S. troops and medevac crews could arrive, he said.

"We offer our heartfelt prayers and condolences to the families of the soldiers involved in this tragic incident," said Lt. Col. Mark Gillespie, the deputy commander of 2nd CAB, in a statement. "Our first priority is to provide their families with the support they need during this difficult time."