South Korea's military said on Monday that North Korean mines deliberately planted inside the Demilitarized Zone (DMZ) caused a blast last month that injured three South Korean soldiers. It said it had carried out a mine-clearing operation at the site in response. The DMZ is a heavily fortified buffer strip that has divided the Korean Peninsula since the 1950-53 Korean War.

Announcing the final results of an investigation conducted jointly with the U.N. Command (UNC), Lt. Gen. Kwon Dae-won, vice chairman of the Joint Chiefs of Staff, said resin antipersonnel mines caused the Sept. 21 explosions. Two soldiers suffered serious ankle injuries and a third was lightly hurt. According to the military, the mines contained TNT and thermosetting resin components consistent with North Korean devices, and fragments taken from the wounded matched plastic mines previously recovered from the Imjin River.

Seoul stressed that the mines were not simply washed south by floods, which it acknowledges is a common occurrence. They were buried about 3 to 10 centimetres underground, and the UNC estimated they were placed roughly 12 months earlier. GPS measurements put both blast sites and a further mine about 10 metres south of the Military Demarcation Line (MDL), the border running through the DMZ. The military removed the minefield at about 12:51 p.m. Monday and said it would continue clearing if the North does not remove its mines. It also demanded a sincere apology from Pyongyang, saying the mines violated the Armistice Agreement, which bans hostile acts within, from or against the DMZ.

Pyongyang rejects the findings. State media reported that Kim Yo-jong, the influential sister of leader Kim Jong-un, called the accusation groundless and a fabrication, said the North had not deliberately planted mines, and warned of retaliation if Seoul takes corresponding action. On Tuesday, defence ministry spokesperson Chung Bin-na said Seoul was preparing a response to press the North for an apology, without giving details. She also called on Pyongyang to hold talks on differences over where the MDL actually lies, acknowledging that the two Koreas view the line differently. Parts of the line, which runs more than 200 km with about 1,900 markers, have become hard to identify after decades of limited access.

The incident comes against a backdrop of rising border tension. North Korea has fortified the frontier since April 2024 with barbed-wire fences, mines and anti-tank barriers, after Kim Jong-un described inter-Korean ties as those between "two states hostile to each other." Seoul says as many as 7,000 North Korean troops may have been mobilised daily for such work, and that northern incursions south of the MDL have exceeded 50 this year, up from nine in 2024 and 17 in 2025. The dispute over responsibility and the line itself leaves the risk of further confrontation along the border unresolved.