On September 21, two mines exploded inside the Demilitarized Zone (DMZ) that divides North and South Korea. Three South Korean soldiers were injured in the blast, two of which suffered serious injuries. 

Two weeks later, on October 5, the South Korean military concluded that the explosion was caused by a mine North Korea had buried south of the Military Demarcation Line (MDL) that serves as a de facto border.

“Based on the results of the joint investigation with the United Nations Command (UNC) and scientific evidence, we have made a final determination that our service members, who were carrying out normal DMZ operations south of the MDL, were seriously injured by a plastic antipersonnel mine that North Korea planted south of the MDL under the pretext of so-called border fortification work,” Kwon Dae-won, deputy chief of the South’s Joint Chiefs of Staff (JCS) said during the military’s press conference on Monday. Both the UNC and the South Korean military assessed that the mines had been buried for at least 12 months. 

Along with Kwon’s briefing, the military also said that it had launched an operation to remove the North Korean mines buried around the explosion site by detonating them. It also urged North Korea to offer a sincere apology to the injured service members and to remove the mines it installed in violation of the Armistice Agreement. 

However, Pyongyang already rejected these findings and then refused an offer of talks on the border when Seoul released its initial assessment on the cause of the land mine explosion days ago. The dispute now places the engagement policy of South Korean President Lee Jae-myung under direct strain.

To understand the issue, it helps to begin with the geography of the border. The MDL separates the two Koreas, and the DMZ extends for two kilometers on either side of it. The Armistice Agreement forbids hostile acts inside the DMZ and bars any crossing of the MDL without permission from the Military Armistice Commission. The U.S.-led UNC holds the authority to judge violations of the armistice.

Nevertheless, the line has grown difficult to read on the ground. Only around 200 of the 1,292 signs placed along it in 1953 remain intact. Seoul’s Defense Ministry has acknowledged that the baselines of the UNC and the South Korean military differ across roughly 60 percent of the border coordinates.

The September 21 explosions occurred during an operation to clear a path for a joint inspection with the UNC. The inspection was meant to examine terrain changes near the MDL, which military officials suspected were signs of mine-laying by North Korea. The blast site lay about 10 meters south of the line.

On September 28, the South’s JCS assessed a very high possibility that North Korean mines caused the explosions. Forensic analysis detected traces of trinitrotoluene and a brown synthetic material consistent with North Korean plastic antipersonnel mines. Next, investigators found another unexploded North Korean mine near the site. As a result, the South Korean military believes the area held at least four mines.

In addition, South Korean Defense Minister Kang Shin-chul told lawmakers on September 29 that Pyongyang appeared to have planted mines at several locations south of the MDL.

On September 30, Lt. Gen. Kang Hyun-woo of the JCS demanded an apology and responsible measures from North Korea, and he urged Pyongyang to halt its border fortification. Meanwhile, the UNC reported that investigators had identified an active North Korean mine south of the line. The command added that it was addressing the violation through established armistice mechanisms. For now, the military has said that it will announce the final results of its joint investigation at a later date.

North Korea answered with a flat denial from Kim Yo Jong, the powerful sister of the North’s autocratic leader Kim Jong Un and the main voice on inter-Korean relations. The Korean Central News Agency (KCNA), one of the North’s key state-controlled media, carried her statement on September 30. 

“The incident is a clear farce reminiscent of the ‘wooden-box mine incident’ which disturbed the world more than ten years ago, in consideration of the time and method of provocation,” Kim said in her statement. “Clearly speaking, our soldiers have never crossed the border.”

On October 2, South Korean Unification Minister Chung Dong-young proposed that the two Koreas should meet to confirm and survey the MDL again. In his view, the fading visibility of the line was a primary factor behind the blast. While Chung said that demanding an apology from North Korea is natural, he opposed resuming loudspeaker broadcasts toward the North as a dangerous step.

Pyongyang replied the same day. Kim Yo Jong rebuffed Chung’s proposal as a “wild dream and unilateral jargon.” 

Her statement then turned to the border line itself. “It is the fixed stand of the DPRK government to define the borderline, our sovereign boundary line, through the full exercise of sovereignty, that is, by the use of force, not by means of negotiation,” Kim said. (DPRK is an acronym of North Korea’s official name: Democratic People’s Republic of Korea.)  

Behind the rejection stands a fortification campaign that North Korea launched in 2024. In late 2023, Kim Jong Un declared that the two Koreas are hostile states. Since then, North Korean troops have installed barbed-wire fences and landmines along the MDL. 

Kim Yo Jong has described the work as a matter of sovereignty with no military purpose. Moreover, her statement published on September 30 said that North Korea had decided to strengthen counterattack capability opposite the 21st Infantry Division of the South Korean army on the eastern front.

South Korean officials counted more than 20 crossings of the MDL by North Korean troops in August alone – more than the 17 cases recorded during all of 2025. A JCS official attributed the crossings to work in unfinished areas. Under the rules of engagement, South Korean forces fire warning shots when North Korean troops cross the line. Pyongyang has threatened swift retaliation should South Korean troops fire directly at North Korean soldiers at work on the border project rather than firing warning shots.

The episode recalls a crisis in 2015 – the same chain of events that Kim Yo Jong mentioned in her own statement. On August 4, 2015, wooden-box mines detonated near the MDL south of Paju and severely injured two South Korean noncommissioned officers. Of the two, one lost both legs and the other lost part of one leg. Six days later, Seoul determined that North Korean troops had deliberately laid the mines.

In response, Seoul resumed loudspeaker broadcasts along the border for the first time in 11 years, and the two sides exchanged artillery fire on August 20. Soon after, senior officials between the two Koreas opened marathon negotiations at Panmunjeom on August 22. Three days later, they reached a six-point agreement. According to the agreement, Pyongyang expressed regret over the explosions and Seoul agreed to halt the broadcasts. The agreement eventually led to further contacts and to reunions of families separated by the 1950-53 Korean War.

Still, the circumstances of 2026 differ from those of 2015. For one, Seoul no longer has loudspeakers along the border because the Lee administration removed them to reduce tensions. For another, Pyongyang has denied responsibility and refused talks. Accordingly, Kang has cautioned against repeating the measures of 2015. 

The contrast matters because Lee has pursued de-escalation since taking office. In August 2025, he pledged to restore the 2018 inter-Korean military agreement. His government suspended loudspeaker broadcasts directed at the North in a unilateral concession. 

A day before Chung made his proposal for inter-Korean talks, Lee discussed the mine blasts in a speech marking the 78th Armed Forces Day. Lee said he still felt pain over the soldiers wounded in the explosions. Moreover, he pledged that his government would keep pursuing practical measures to lower military tensions with Pyongyang. Lee’s tone contrasted with the warning of retaliation that the North’s state media had published a day earlier. 

In this context, many critics in South Korea wondered why Seoul chose to keep to its dovish stance on Pyongyang even after North Korea caused injuries to three South Korean troops., Seoul has stated that it will “take necessary measures” after establishing the facts based on the investigations; however, the military has not yet specified what corresponding measures it would take.

Meanwhile, North Korea fired a ballistic missile toward the waters off its east coast from the Wonsan area on October 3. The launch came one day after Kim Yo Jong ruled out any contact with Seoul. The JCS said that the missile flew more than 700 kilometers. However, KCNA claimed on October 4 that the missile, which was reported as an intermediate-range strategic missile, hit a target 1,000 kilometers away. 

“We must continue our responsible efforts nonstop to constantly and repeatedly make the enemy recognize the reliability and fatality of our strategic offensive means,” Kim Jong Un said. 

A separate announcement by Kim Yo Jong on October 3 addressed the flight distances reported by South Korea and Japan. She said that those figures exposed the limits of the tracking capability of the two militaries. In her account, a wave-like flight path caused the enemy to lose the missile from its first skip points. She described the missile as able to change its orbit at low altitude and said it was equipped with artificial intelligence. 

“The enemy always made such a lame excuse that there is a limit to the detection capability because of the curvature of the earth’s surface, but in fact this just serves as a proof of our perfect missile capability and the most scientific ‘evaluation index’ confirming the power and reliability of our weapon system,” Kim said. “In other words, this means that there is no way to avoid this attack.”