A U.S. Army Apache helicopter crashed in central South Korea on Monday during a training mission, killing two pilots aboard, police and military officials said.

The attack helicopter went down in the county of Wonju in Gangwon province, officials said.

The helicopter was assigned to the Second Infantry Division of the U.S. Army, said Captain Jeff Davis, a Pentagon spokesman.

"This happened during a routine training mission and sadly did kill both pilots," Davis said. "The cause is currently under investigation."

The identities of the pilots were being withheld pending notification of their families.

About 28,500 U.S. troops are stationed in South Korea in joint defense with the South's forces against North Korea. The two Koreas are in a technical state of war under a truce after their 1950-53 Korean War.

On Monday, South Korea's military conducted artillery live-fire drills on islands near a disputed maritime border with North Korea, ignoring Pyongyang's threat to fire back if any of the shells landed in its waters.