A composite image shows, from left, the Defense Ministry flag, a view of the Demilitarized Zone and the United Nations Command flag. (Yonhap and UNC) South Korea’s Defense Ministry has lodged concerns with the United Nations Command over its handling of North Korea’s activity inside the Demilitarized Zone, sources said Tuesday.The move came after the South Korean military detected signs that North Korean troops had expanded border fortification work to areas within 100 meters of the Military Demarcation Line, including the installation of fences and land-clearing activity believed to be linked to mine-laying operations.A Defense Ministry official speaking on condition of anonymity said that the ministry recently conveyed its concerns to the UNC after identifying signs that North Korea was carrying out border fortification work in areas less than 100 meters north of the MDL.“The ministry has asked the UNC to take a more active and substantive response to North Korea’s border fortification work,” the official said.Asked about the matter, the ministry said it could not confirm details, citing “military and diplomatic matters between South Korea and the United States.”Seoul views the activity as a violation of the 1953 Armistice Agreement, which halted hostilities in the 1950-53 Korean War, and has said it will work with the UNC, which oversees the armistice regime, to respond to the North’s actions.But the command has taken a more cautious position, saying Pyongyang’s construction and defensive measures do not automatically constitute a breach of the armistice.North Korea has been reinforcing its side of the border since April 2024, after leader Kim Jong-un defined inter-Korean relations in December 2023 as those between “two hostile states.” The work has included clearing land, laying mines and installing fences in the DMZ.In some areas, North Korean barbed-wire fences have reportedly been installed just 80 to 90 meters north of the MDL. Land-clearing work believed to be linked to mine-laying has also been detected as close as 5 to 10 meters from the line.The Defense Ministry has determined that such activity near the MDL amounts to a violation of the armistice.“The North Korean military’s installation of obstacles near the MDL is a clear violation of the Armistice Agreement,” ministry spokesperson Chung Binna said during a press briefing Monday. “Our military will continue to respond in close cooperation with the United Nations Command.”The armistice states that neither side shall commit any hostile acts within, from or against the DMZ. The buffer zone extends 2 kilometers north and south of the MDL and is subject to the armistice regime.The UNC, however, has indicated that it does not view all construction activity inside the DMZ as an armistice violation, particularly when such work appears to be defensive in nature.“Construction, fortification and other defensive measures do not automatically constitute violations of the Armistice Agreement,” the command said in a statement Monday.A separate ministry official said there is growing unease within the South Korean government that the UNC has been strict in asserting its authority over the southern side of the DMZ, while appearing more restrained in responding to North Korean activity inside the buffer zone.“When South Korea tries to do something in the DMZ, the UNC acts as if it is firmly within its jurisdiction,” the official said. “But when North Korea takes steps that could undermine the armistice regime, the command appears far more cautious. There is a sense that the UNC is stricter toward South Korea than toward the North.”The issue touches on a broader and long-running dispute over control of access to the DMZ.In December last year, Unification Minister Chung Dong-young criticized the UNC’s control over DMZ access after a senior presidential security official was denied entry to a war remains excavation site at White Horse Ridge inside the buffer zone.At the time, Chung said such restrictions raised questions about South Korea’s sovereignty and the scope of the UNC’s authority.The incident later fueled calls within the ruling Democratic Party of Korea to revise rules governing nonmilitary access to the DMZ, including proposals that would give the South Korean government a greater role in approving visits for purposes such as peace, ecology and historical projects.Seoul has said it respects the UNC’s authority under the armistice, while calling for more practical arrangements in managing parts of the heavily fortified border.The UNC has opposed any move that would weaken its control over DMZ access, arguing that entry into the buffer zone remains subject to its authority under the armistice.