State-run media said North Korea "abrogates all agreements on nonaggression reached between the North and the South ... and also notifies the South side that it will immediately cut off the North-South hotline."
Pyongyang's statement appears to refer to the bilateral pact signed in 1991 that endorses the peaceful settlement of disputes and the prevention of accidental military clashes. However, earlier this week the North also reiterated threats to walk away from the 1953 armistice that technically ended the Korean War.
Also this week, Pyongyang threatened to launch a pre-emptive nuclear strike against the U.S. and its allies.
(As Reuters notes, while the threat of a strike against the U.S. is "a hollow one," South Korea and Japan are in easy range of the North's short- and medium-range missiles.)
The stepped up rhetoric from Pyongyang is the latest in a week of bellicose posturing in the lead-up to the United Nations Security Council's unanimous approval on Thursday of sanctions to tighten trade and financial restrictions on the North in an effort to force it to halt its nuclear weapons program.
Even so, as The Associated Press points out, sanctions have done little to deter Pyongyang thus far:
"Since 2006, North Korea has launched long-range rockets, tested a variety of missiles and conducted three underground nuclear explosions, the most recent on Feb. 12. Through it all, Pyongyang was undeterred by a raft of sanctions — both multilateral penalties from the United Nations and national sanctions from Washington, Tokyo and others — meant to punish the government and sidetrack its nuclear ambitions."
The war of words is testing South Korea's new president, Park Geun-hye, who campaigned on a promise to remain vigilant while keeping the door open for the possibility of ending the long conflict on the peninsula.
Speaking at a graduation ceremony for South Korean military cadets on Friday, Park promised to "deal strongly with North Korea's provocations."
The early days of Park's administration could prove dangerous, according to the Center for Strategic and International Studies.
A CSIS analysis suggests a causal link between a change in South Korean leadership and "a military provocation of some form within weeks."
North Korean leader Kim Jong Un, center, walks with military personnel as he arrives to inspect a military unit on Mu Islet, near the border with South Korea.
(Korean Central News Agency / Associated Press / March 7, 2013)
North Korean leader Kim Jong-Un (C) talks with officers at a guard post during his visit to the Jangjae Islet Defence Detachment and Mu Islet Hero Defence Detachment on the front, near the border with South Korea, southwest of Pyongyang.
March 7, 2013 released by the North's official KCNA news agency in Pyongyang March 8, 2013.
(Reuters / Korean Central News Agency)
A North Korean soldier reacts as he patrols along the Yalu River near the Chinese border last month.
(Mark Ralston / AFP / Getty Images via NPR)
More coverage on this (these are also additional sources as referenced at the source):
LA Times: North Korea vows to end nonaggression pacts with South Korea
Reuters: North Korea can't hit America, but South Korea and Japan in range
BBC News: North Korea: Will new UN sanctions persuade or provoke?
Associated Press: UN Sanctions May Play Into North Korean Propaganda
Center for Strategic and International Studies (CSIS): UN Security Council Passes New Resolution 2094 on North Korea
Source: NPR the two way