North Korea has sent a letter to the president of the U.N. Security Council (UNSC) calling last month's land mine blast near the border an incident "fabricated" by South Korea, Pyongyang's state media reported Monday. The North's move came less than a week after South Korea sent to the council its own letter calling on North Korea to apologize for the Sept. 21 mine blast that injured three South Korean soldiers and take responsibility for its violation of the Armistice Agreement. The letter, sent Sunday by Pyongyang's permanent representative to the United Nations, said Seoul "fabricated" the mine blast in the Demilitarized Zone (DMZ) as a "sinister" attempt to "impede" the North's border fortification work, according to the Korean Central News Agency (KCNA). The North described the fortification a "legitimate and just exercise of its sovereignty going in strict conformity with the U.N. Charter and international law as it is a self-defensive measure to defend its territorial security from outside threat of aggression." It also accused the South Korean military of firing warning shots at