North Korea accused South Korea of fabricating last month's land mine explosions inside the DMZ in a letter to the president of the U.N. Security Council, state-run media reported Monday.

SEOUL, Oct. 26 (UPI) -- North Korea accused South Korea of fabricating last month's land mine explosions inside the Demilitarized Zone in a letter to the president of the U.N. Security Council, state-run media reported Monday.

The North's permanent representative to the United Nations sent the letter Sunday, the official Korean Central News Agency reported.

South Korea sent its own letter to the council Thursday, outlining its investigation into the explosions and accusing North Korea of violating the armistice agreement that halted the 1950-53 Korean War.

The Sept. 21 explosions injured three South Korean soldiers, two seriously. Seoul's military concluded that North Korean troops had planted the mines south of the Military Demarcation Line, the military boundary separating the two Koreas, a finding Pyongyang has rejected.

The North's letter said that South Korea "fabricated" the mine blasts as a "sinister obstructive move" to delay and impede the North's ongoing fortification work along its southern border, KCNA reported.

It defended the construction as a "legitimate and just exercise of its sovereignty" and a self-defense measure against outside aggression.

North Korea began the extensive construction effort after leader Kim Jong Un declared inter-Korean relations to be those of "two hostile states" in late 2023. Since April 2024, the work has included clearing land, reinforcing tactical roads, installing anti-tank barriers and laying mines.

South Korean lawmakers briefed by the military said Friday that the North had planted an estimated 960,000 land mines along the inter-Korean border since 2024.

The letter also accused the South Korean military of "opening fire on our service personnel involved in the border fortification project," calling it a violation of the U.N. Charter's prohibition on the threat or use of force against another country's territorial integrity.

South Korea's military has issued warning broadcasts and fired warning shots when North Korean troops crossed the MDL during border construction work.

"I remind you that if the ROK invades the territory of our country even a millimeter or perpetrates a direct provocation doing harm to our personnel's safety and lives, the DPRK is legally entitled to exercise the right to self-defense," the letter said, using the official acronyms for South and North Korea, respectively.

Seoul has said differing understandings of the boundary's precise location have increased the risk of accidental clashes.

On Friday, South Korea proposed military talks with Pyongyang to jointly verify the line, restore military communication channels and discuss ways to prevent border confrontations.