American veterans of the Vietnam War have helped the Communist country locate a mass grave of 81 of its soldiers who died in battle more than 40 years ago, the Vietnamese military said Wednesday. Authorities have dug up the bones of the North Vietnamese soldiers in the Central Highlands province of Kon Tum, hoping to return them to their families. The soldiers are believed to have died during an attack on a U.S. base in the area in March 1968, Vietnamese army Lt. Col. Tran Van Khanh said. They were buried by the Americans. Decades later, U.S. veterans who served at the base gave Vietnamese authorities a map to the mass grave. Khanh said the remains of four soldiers have been identified and returned to their families, while the remaining 77 unidentified sets of remains were buried in a local military cemetery Wednesday. About 58,000 U.S. troops and 3 million Vietnamese died in what is known here as the American War. The conflict ended in 1975 after U.S. troops were withdrawn and North Vietnam's Communist forces overran Saigon, the capital of U.S.-backed South Vietnam. Washington and Hanoi established diplomatic relations in the early 1990s and now cooperate in searching for soldiers missing in action on both sides.