Kim Jong Un’s powerful sister Kim Yo Jong on Wednesday rejected South Korean findings that North Korea planted land mines that injured three South Korean soldiers last week, warning that Pyongyang would retaliate if the South fires at North Korean troops carrying out border fortification work.

Three South Korean military officers were injured in two successive explosions on Sept. 21 near the military demarcation line in the western section of the Demilitarized Zone (DMZ), the heavily fortified buffer zone separating the two Koreas.

Kim Yo Jong’s statement came after South Korea’s Joint Chiefs of Staff (JCS) on Monday announced a preliminary assessment that North Korean mines caused the explosions following a joint inspection of the site with the U.S.-led United Nations Command.

The South Korean military said its investigators and U.N. personnel found another North Korean mine during a follow-up inspection Tuesday. The U.N. Command said Wednesday that North Korea had violated the armistice agreement that ended the 1950-53 Korean War. It said the violation was being addressed through established mechanisms but provided no further details.

South Korean Defense Minister Kang Shin-chul has said Seoul would consider unspecified “corresponding measures” if a full investigation confirms North Korea was responsible for the blasts.

Kim Yo Jong, a senior foreign policy official for her brother and possibly the second-most powerful figure in Pyongyang, described South Korea’s assessment as a “conspiratorial farce.” She accused Seoul of making groundless allegations to create a pretext for military provocation against North Korea.

North Korea has in recent years installed mines, anti-tank barriers and other fortifications along its front line as relations between the two Koreas have sharply deteriorated. The developments have raised concerns in South Korea over the growing presence of North Korean troops near the border.

Reading a statement on television, Kang Hyunwoo, chief director of operations at South Korea’s JCS, said the military “strongly urges” North Korea to apologize for the explosions and take “responsible measures” to prevent similar incidents.

He also called on Pyongyang to immediately stop its border fortification work and other actions that increase tensions.

“We clearly state that North Korea bears full responsibility for any future developments,” he said.

Kim, however, defended North Korea’s border fortification activities as a legitimate exercise of its sovereignty. She accused South Korea of escalating tensions by issuing warnings and firing warning shots at North Korean troops engaged in the work, while insisting that “our soldiers have never crossed the border.”

“When a single bullet is hit on our land, they must be prepared for a lot,” she said. “If the (South Korean) military gangsters fire at our soldiers carrying on the permanent project for the southern border, not warning shots, our border units will take immediate and merciless retaliatory action.”

The explosions occurred about 10 meters south of the military demarcation line during an operation to establish a patrol route through a densely vegetated area that had rarely been visited for decades.

The route was intended to facilitate future inspections with the U.N. Command after South Korea detected “terrain changes” since last year that it believed could have resulted from North Korean mine-laying.

Kwon Dae-won, vice chairman of South Korea’s JCS, said there was a “very high possibility” that North Korean mines caused the explosions, noting that there was no record of South Korean or allied forces laying mines in the area.

He said blast marks, forensic analysis of explosive substances and what appeared to be a third North Korean mine found at the scene also pointed to the North. Kang said South Korean and U.N. investigators found a possible fourth mine during Tuesday’s follow-up inspection.

The DMZ stretches 248 kilometers (155 miles) and is about 4 kilometers (2.5 miles) wide, making it one of the world’s most heavily fortified borders. An estimated 2 million mines are buried in and around the zone, which is also protected by barbed-wire fences, tank traps and combat troops on both sides.

The zone is a legacy of the Korean War, which ended with an armistice rather than a peace treaty.

The latest explosions came more than a decade after South Korea blamed North Korea for land mine blasts that maimed two South Korean soldiers and sharply heightened tensions between the countries in August 2015.

The two Koreas subsequently exchanged threats, conducted weapons demonstrations and resumed border propaganda broadcasts. Days of marathon negotiations eventually pulled the countries back from the brink. North Korea issued a vague expression of regret over the soldiers’ injuries but never explicitly accepted responsibility.

Last week’s explosions came as South Korea’s liberal government sought to revive diplomacy between Pyongyang and Washington as part of broader efforts to ease tensions on the Korean Peninsula.

Since early 2024, North Korea has adopted an increasingly hard-line position toward South Korea, declaring it a permanent enemy and abandoning the concept of shared statehood in favor of a hostile “two-state” system.

Pyongyang has so far rejected U.S. calls to resume diplomacy, which collapsed in 2019, insisting that Washington must first abandon its demand for North Korean denuclearization as a condition for talks.