North Korea threatened to take "strong physical countermeasures" Friday if South Korea takes part in enforcing United Nations sanctions, which it called a "declaration of war."
The United Nations Security Council resolution approved unanimously on Tuesday condemns North Korea for launching a rocket in December.
"Sanctions mean war and a declaration of war against us," the Committee for Peaceful Unification of the Fatherland said in a statement carried by North Korea's official Korean Central News Agency.
South Korea's President-elect Park Geun-hye has left open the door for dialogue with Pyongyang.
During her election campaign, Miss Park said she would consider economic assistance to North Korea on the condition that Pyongyang makes a commitment to denuclearize the Korean Peninsula.
Miss Park will not tolerate North Korean provocations, remains committed to pushing for dialogue with Pyongyang, a special envoy to the president-elect said on Friday.
"President-elect Park makes it clear that North Korea's nuclear ambitions and further provocations against the South will not be tolerated," Rhee In-je told the Associated Press. "In particular, she strongly urges North Korea to refrain from further worsening the situation by conducting a third nuclear test."
"It is difficult for me to see any improvement in inter-Korean relations until the North Korean leadership changes its thinking and policy orientation," said Daniel Pinkston, the Seoul-based deputy project director of International Crisis Group's Northeast Asia program.
On Thursday, North Korea said it would conduct a nuclear test and launch long-range rockets in response to the U.N. resolution.
The Obama administration's top official for North Korea, Glyn Davies, said a North Korean nuclear test would be a "mistake," "a missed opportunity" and "highly provocative."
"It is clear that North Korea's actions have created an environment where it is harder for the other parties to reach out," said Scott Snyder, director of the Program on U.S.-Korea Policy at the Council on Foreign Relations.
North Korea's National Defense Commission said a nuclear test and the launch of long-range rockets would be a "new phase of the anti-U.S. struggle that has lasted century after century, will target against the U.S., the sworn enemy of the Korean people."
"Settling accounts with the U.S. needs to be done with force, not with words as it regards jungle law as the rule of its survival," the commission said in a statement carried by KCNA.
The U.N. resolution warned of "significant" action if North Korea conducts another nuclear test.
North Korea has twice conducted nuclear tests -- in 2006 and 2009 -- in response to U.N. sanctions punishing it for launching rockets.
Recent photographs of the Punggye-ri nuclear test site in northeastern North Korea show that the site is in a state of readiness.
Pyongyang did not offer any timeframe for its plans. However, once the order is given, a nuclear test could take place within a matter of weeks, say analysts.
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