With the North's belligerence growing over the latest ratcheting up of U.N. sanctions over its Feb. 12 underground nuclear test, the country's official Korean Central News Agency quoted the Committee for the Peaceful Reunification of Korea as saying: "The DPRK [or the Democratic People's Republic of Korea, the official name of North Korea] abrogates all agreements on non-aggressions reached between the North and the South."
South Korea's Yonhap News Agency described the committee as a propaganda outfit against Seoul.
"The DPRK will close the Panmunjom liaison channel between the North and the South [the main border crossing point]," the committee said.
The report said South Korea also would be informed about the North's decision to immediately cut off the North-South hotline.
The North already has said it would scrap the 1953 armistice agreement that ended the 1950-1953 Korean War.
Separately, Kim Jong Un, who took over as North Korea's leader after the death of his father in December 2011, said his military was ready to fight an all-out war, China's Xinhua News Agency reported, quoting the KCNA.
"All the service personnel of the ground, naval, air and anti-air and strategic rocket forces are fully ready to fight a Korean style all-out war," the leader said while inspecting a front-line army unit stationed on two southwestern islands.
Kim warned he would "issue an order to start the just great advance for national reunification" if "the enemy makes any slight reckless provocation against the DPRK."
The threat to scrap the 1953 armistice agreement came as the United States-South Korea planned their "Key Resolve" military exercise. North Korea has said the exercise is a prelude to an invasion.
The tour by Kim, who is also the supreme commander of the Korean People's Army, was to the military units responsible for the November 23, 2010 shelling of South Korea's Yeonpyeong Island in which four people died and 16 were wounded.
He was quoted as saying the artillery attack annihilated South Korean warmongers' efforts to provoke the North, Yonhap reported.
Other recent threats from the North have included preemptive nuclear strikes against its "aggressors" and turn them into a "sea of fire."
The unanimously approved U.N. Security Resolution 2094 comes in the wake of its January action, tightening its sanctions over the North's earlier two nuclear tests in 2003 and 2006, its missile tests and its long-range rocket firing last December. Resolution 2094 came after Untied States reached a deal with China, which is North Korea's closest ally.