One border, 3 lines: Why another DMZ mine blast could be waiting to happen

North Korean soldiers stand in front of the 204th stake of the Military Demarcation Line as the UN Command Military Armistice Commission arrives for an inspection in 1959. At the time, the UNC and North Korea divided up the management of the 1,292 stakes between them, using them as markers to show the MDL’s exact location. Only 181 of the stakes currently remain, making it difficult to identify the MDL through the stakes. (courtesy of the National Archives of Korea)

The Sept. 21 mine explosion in the western Demilitarized Zone (DMZ) has emerged as a major point of contention between the two Koreas. Seoul maintains that the incident constitutes a clear violation of the Armistice Agreement, while Pyongyang rejects the allegation, dismissing the explosion as a fabricated farce staged by the South.

“This is a clear violation of the Armistice Agreement. We believe this is related to North Korea’s attempts to fortify the border,” South Korean Defense Minister Kang Shin-chul stated before the National Assembly National Defense Committee on Sept. 29. 

“Clearly speaking, our soldiers have never crossed the border,” said Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, in a statement issued on Sept. 30. 

South Korea said North Korean soldiers buried a mine 10 meters south of the Military Demarcation Line (MDL), which Seoul described as a violation of the Armistice Agreement.

Kim retorted by saying that the South Korean military should think “first of all about what the world will say about its inability to distinguish its own land and other’s land.” 

The two Koreas’ conflicting claims stem in large part from their fundamentally different interpretations of the Military Demarcation Line (MDL), which serves as the land border between North and South. 

Some may argue that the MDL is clearly marked on the map attached to the Korean Armistice Agreement and that, with today’s advanced GPS technology, its exact location should be impossible to miss.

But the width of the stroke used to mark the MDL on the 1:50,000-scale map attached to the Armistice Agreement has a margin of error of around 50 meters. 

A follow-up agreement to the Armistice Agreement set up 1,292 stakes as markers to pinpoint the exact location of the Military Demarcation Line, defining the MDL as an invisible line running between the stakes.

At the time, the stakes were spaced roughly 200 meters apart, making it possible to identify the boundary by sight alone. Today, however, only 181 remain. With the surviving stakes now a couple of kilometers apart, they no longer represent an adequate means of determining the boundary.

Soldiers from North and South Korea verify the removal of guard posts on each side of the Demilitarized Zone on Dec. 12, 2018, as part of a buffer-creating inter-Korean military agreement. (via Presidential Archives)

Even satellite navigation coordinates cannot readily establish the location of the MDL. The South Korean military uses the US-developed Global Positioning System (GPS) while North Korea uses Russia’s GLONASS satellite navigation system, with the two systems sometimes producing contradictory coordinates for the same location.

“In December 2018, [representatives from] both sides were supposed to meet at the MDL to inspect guard posts that both sides had provisionally abandoned under the Comprehensive Military Agreement,” said Cho Yong-geun, who formerly served as the director for North Korea policy at the Ministry of National Defense.

“But because the two sides’ satellite navigation systems gave different coordinates, they were unable to specify where to make contact. In the end, a yellow flag measuring 3 by 2 meters was raised to mark the meeting place,” Cho said.

With so many of the boundary markers missing, South Korea, North Korea and the United Nations Command (UNC) have each drawn their own reference lines, effectively creating three different versions of the MDL.

In 2004, the South Korean military, working with the US National Geospatial-Intelligence Agency, aligned the MDL as it appears on the original armistice maps with the actual terrain, establishing its own coordinate line for the MDL on military maps.

That line was applied to South Korean military maps in 2011 and updated in 2014 and 2015. Front-line units give priority to identifiable stakes but also use prominent terrain features such as large rocks and streams as reference points when plotting the MDL on maps and operational displays.

Between 2014 and 2016, the UNC Military Armistice Commission brought in terrain analysts from Korea, the US and the UK on three occasions to determine the MDL by analyzing its location on the armistice maps and surveying the remaining stakes. In May 2016, the UNC finalized its version of the MDL, which the South Korean military calls the “UNC reference line.”

The Korean military’s and UNC’s maps are said to differ on roughly 60% of the MDL.

“There are cases where the South Korean military says that North Korean troops crossed the MDL, only for the UNC to respond that no crossing occurred. So the Joint Chiefs and UNC are discussing how to at least get our own lines to match,” said an official from South Korea’s Joint Chiefs of Staff.

North Korea also has its own version of the MDL.

Defense Minister Kang Shin-chul appears before the National Assembly’s National Defense Committee on Sept. 29, 2026, regarding the explosion of land mines in the DMZ. (Yonhap)

When Kim Yo-jong said in a recent statement that “our soldiers have never crossed the border,” she was arguing that North Korea had planted the mines on its own territory north of the MDL, which therefore would not constitute a violation of the armistice.

It seems that North Koreans have a similar struggle with determining the MDL’s precise location.

“When North Korean troops working in the DMZ cross over the MDL, we warn them with broadcasts and warning shots. The next time they come, they invariably bring maps and binoculars to check their location and, in some cases, change their worksite,” a Joint Chiefs official said.

Some think the two Koreas should reconcile their differing versions of the MDL to prevent another incident like last month’s land mine explosion.

South Korean Unification Minister Chung Dong-young proposed inter-Korean dialogue with the North to resolve the issue on Oct. 2, noting that “in the end, the fundamental issue is the discrepancy” between these varying versions of the MDL.

“At the very least, we need to resume communication to reconfirm and establish the MDL,” he said.