South Korea said on Monday that a September 21 mine blast in the Demilitarized Zone that seriously wounded two of its soldiers was caused by mines planted by North Korea. The finding came from a joint investigation with the United Nations Command.

Vice Chairman of the Joint Chiefs of Staff Kwon Dae-won said the blast was caused by an anti-personnel mine installed south of the Military Demarcation Line during North Korea’s fortification work. Tests found TNT and resin components consistent with North Korean mines. The mines were buried 3 to 10 cm deep and were likely planted about a year ago.

Seoul urged Pyongyang to apologise and remove the mines, which it called a violation of the armistice agreement. The South’s military cleared the minefield on Monday.

North Korea’s Kim Yo Jong dismissed the accusation as groundless. The two Koreas remain technically at war, as the 1950-53 conflict ended in an armistice, not a peace treaty.