South Korean Ambassador Park In-kook listens during a UN Security Council vote to adopt new sanctions on North Korea in June 2009. South Korea has had difficulty engaging the North in discussion over its nuclear program as talks have repeatedly stalled.

North Korea threatened Friday to break off all dialogue and negotiations with South Korea in anger over Seoul's alleged contingency plan to deal with potential unrest in the communist country.

The National Defence Commission — the North's most powerful state organ headed by leader Kim Jong-il — also warned the North will initiate a "sacred nationwide retaliatory battle" against South Korea over the plan, which the North claims is aimed at toppling its regime.

The rare statement from the commission comes amid diplomatic efforts to revive stalled international talks on ending Pyongyang's nuclear weapons programs. It also comes as North Korea has offered conciliatory gestures to the South, including one Thursday to discuss restarting stalled tour programs.

North Korea stopped short of saying whether it will push for Seoul's exclusion in the broader disarmament talks that involve the U.S., China, Russia, Japan and South Korea, which Pyongyang is boycotting.

N. Korea asks for apology

The statement also said, however, that South Korea could still salvage dialogue by apologizing to the North for what it called unspecified "crimes" against it.

Paik Hak-soon, an analyst at the Sejong Institute, a private security think-tank near Seoul, said the North was issuing a warning that it may not talk to South Korea in future disarmament negotiations as it did to Japan in some previous rounds.

The North said once the plan is completed and put into practice "a sacred nationwide retaliatory battle to blow up the stronghold of the South Korean authorities," including the presidential office, will begin, said the statement carried by the country's official Korean Central News Agency.

S. Korea denies existence of contingency plans

North Korea occasionally issues statements that include threats to destroy South Korea. Authorities in Seoul monitor them carefully though usually take them in stride.

The statement also urged South Korea to punish those who engaged in drafting the plan while demanding South Korea disband its top spy agency and the Unification Ministry, which handles inter-Korean affairs.

South Korea has recently modified its administrative contingency plans in the event of turmoil in the North including a possible coup, a popular uprising or massive defections, South Korea's mass-circulation Chosun Ilbo newspaper reported earlier this week, citing an unidentified government official.

Unification Ministry spokesman Chun Hae-sung expressed deep regret Friday over the North's rhetoric, which he said was driven by unconfirmed media reports.

South Korea has also reportedly drawn up a military operations plan with the United States to cope with possible emergencies in North Korea. South Korea's Defence Ministry has consistently declined to comment about the existence of such a plan.

S. Korea to deliver food aid

The North's warning came just two hours after it told the South it will accept over 9,000 tonnes of South Korea's previous food aid offer, said Chun.

The North's state media did not mention the food aid.

For a decade, South Korea was one of the biggest donors to the North before President Lee Myung-bak took office in 2008 with a pledge to get tough on the North and halted unconditional assistance.

The North's latest threat called into question its recent overtures toward South Korea and marked a clear departure from its New Year Day's commitment to improve relations.

On Thursday, the North proposed holding talks with South Korea later this month on restarting joint tour programs stalled over the shooting death of a southern tourist and Pyongyang's anger over Seoul's hard-line policies.

"The North sent conflicting signals to the South," said Paik, noting Friday's warnings would have negative implications for inter-Korean relations.

The two Koreas remain technically at war because the 1950-53 Korean War ended in a truce, not a peace treaty.