SEOUL, South Korea — The remains of thousands of American soldiers killed in North Korea during the Korean War are in danger of getting lost after being moved from their burial sites because of various construction work, the North said Monday.

The troops’ remains were neglected and “carried away en masse due to construction projects of hydropower stations, land rezoning and other gigantic nature-remaking projects, flood damage, etc.,” a spokesman for the North Korean military said in a statement carried by the official Korean Central News Agency.

The 1950-53 Korean War, during which the United States fought for South Korea, ended not in a peace treaty but in a truce, leaving the peninsula technically at war. Still, the United States and North Korea conducted 33 joint search and recovery operations at some of the old battle sites in the reclusive North from 1996 to 2005, when Washington withdrew its personnel, citing security concerns amid rising tensions over the North’s nuclear weapons program.

From those operations, the United States recovered what are believed to be the remains of 229 American soldiers missing in action, 107 of them thus far accounted for through DNA tests. Separately, from 1990 to 1994, North Korea unilaterally handed over 208 boxes of remains, some of them commingled, saying they contained the remains of as many as 400 American soldiers. So far, 104 soldiers have been identified from the remains.