What is North Korea building at the border?

The 250km border is already fortified but not in the way many might traditionally think. It is more of a buffer than a barrier at the moment, in the form of a 4km-wide demilitarised zone (DMZ) which runs across the Korean peninsula.

Since 2024, the North is thought to have laid about 960,000 mines in the DMZ, close to half of all the mines thought to be in an area that is already one of the most heavily mined places on earth.

North Korea has also been constructing a continuous physical barrier on its side of the zone, along the full length of the line. It is made up of wire fencing, alongside minefields, tactical roads, and anti-tank barriers laid on ground stripped of vegetation. South Korea’s joint chiefs of staff say the ground-clearing is nearly finished while the construction work is 40-60% complete, and expect it to be finished by the second half of 2028.

Under the 1953 armistice that halted but did not end the Korean war, the DMZ was to be cleared of military forces and equipment.

Why is Kim Jong-un doing this?

Kim Jong-un has abandoned the once-cherished goal of reunification. As recently as 2018, the leaders of the two sides met at the border, and their athletes marched together at the Winter Olympics. But in December 2023, Kim redefined the South as a separate, hostile state, and the construction began a few months later.

Experts in Seoul read Kim’s U-turn as removing the contradiction that lay in threatening nuclear war on people who the North had once called compatriot. When engagement with Seoul collapsed and Moscow emerged as a patron, Pyongyang was left free to press for recognition as a nuclear state.

They also say the construction achieves several goals: stopping North Koreans leaving, slowing any South Korean advance in the event of a return to warfare, and turning the frontier into something that works as an international border.

Kim Yo-jong has said the work will eliminate the danger of a conflict at the border. However, analysts argue the opposite: that the new artillery and missile units being installed make an accidental clash more likely to escalate.

Why are tensions rising now?

On 21 September, three South Korean soldiers were wounded by a landmine blast while clearing a path inside the DMZ. One soldier lost his foot.

South Korea’s military concluded the blast was caused by a North Korean mine placed south of the border, and Seoul has demanded an apology. Pyongyang denied any responsibility for the incident and called it a “self-staged farce”.

South Korea says North Korean troops have repeatedly crossed the border during the work to fortify their side of the line, leading to warning shots that Pyongyang says are provocations by “armed rogues”.

Kim Yo-jong, the powerful sister of the North Korean leader, has since issued about 10 statements in less than a month criticising the South, a frequency Seoul’s unification ministry called unusual. She recently said the North’s propaganda loudspeakers would be ready to blast across the border within days.

Does anyone know where the border actually runs?

No. The armistice drew the military demarcation line (MDL) on maps at a scale of 1:50,000, where a line just a millimetre wide covers about 50 metres of ground. A total of 1,292 numbered markers were then planted to fix it in place, but only about 200 are still identifiable.

So each side has reconstructed it following its own methodology. Seoul works from mapping aligned with the US National Geospatial-Intelligence Agency, while the US-led UN Command (UNC), which oversees the armistice, uses its own survey from a decade ago. North Korea is believed to simply connect the markers it can still see. South Korea’s defence ministry has found that its line and the UNC’s disagree at about 60% of the points they have compared, by tens of metres in places. It is unclear how differently the two Koreas read the line.

North Korean troops reportedly crossed the border about 50 times in August and September this year alone, compared with 17 instances in 2025.

Is anything being done to resolve the border issue?

Seoul is trying. It has proposed talks to confirm jointly where the MDL runs, restore military communication channels severed in 2023 and agree how to avoid accidental clashes. It is the second such offer in a year. Pyongyang ignored the first.

South Korea’s defence ministry calls the work an armistice violation and has demanded that it stop. The UNC, on the other hand, has said that construction and fortification do not automatically constitute violations, and that each case has to be judged on its facts.