South Korea’s military says North Korean mines are the likely cause of a September 21 explosion inside the Demilitarised Zone that injured three South Korean soldiers, two of them seriously.

The blast occurred about 10 metres south of the Military Demarcation Line as soldiers were on patrol. A joint investigation found fragments consistent with North Korean-made mines, according to Seoul’s Joint Chiefs of Staff.

The incident has renewed attention on the heavily mined border, where North Korea has in recent years added anti-tank barriers, planted mines and torn up inter-Korean roads. Pyongyang has not commented on the findings.

South Korea says its troops responded in line with protocol and that it is monitoring the border for further activity. The DMZ remains one of the most densely mined areas in the world despite decades of intermittent clearance efforts.

The four-kilometre-wide DMZ has been laced with landmines since the 1950-53 Korean War, and periodic floods can shift devices into unexpected areas. Joint demining work by both Koreas briefly began in 2018 but stalled as relations soured, leaving the border one of the most hazardous military frontiers on earth.