Park is strongly urging North Korea to refrain from conducting a nuclear test that could only worsen the tensions on the Korean Peninsula in the wake of a provocative long-range rocket launch in December, envoy Rhee In-je told The Associated Press and selected news outlets in Davos, Switzerland.
"President-elect Park makes it clear that North Korea's nuclear ambitions and further provocations against the South will not be tolerated," Rhee said on the sidelines of the World Economic Forum on Thursday. "In particular, she strongly urges North Korea to refrain from further worsening the situation by conducting a third nuclear test."
North Korea responded Friday by warning South Korea of "strong physical countermeasures" if Seoul takes part in U.N. sanctions aimed at punishing Pyongyang for the rocket launch.
"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.
The latest warning comes in the wake of a U.N. Security Council decision Tuesday to condemn North Korea's Dec. 12 rocket launch as a violation of a ban against missile activity. The council, including Pyongyang ally China, also expanded sanctions against the regime.
North Korea's National Defence Commission responded by declaring that the regime is prepared to conduct a nuclear test in defiance of U.N. punishment, and it made clear that its long-range rockets are designed to carry not only satellites but also warheads aimed at striking the United States.
The commission, North Korea's top governing body led by leader Kim Jong Un, pledged Thursday to keep launching satellites and rockets and to conduct a nuclear test as part of a "new phase" of combat with the United States, which it blames for leading the U.N. bid to punish Pyongyang. It said a nuclear test was part of "upcoming" action but did not say exactly when or where it would take place.
"We do not hide that a variety of satellites and long-range rockets which will be launched by the DPRK one after another and a nuclear test of higher level which will be carried out by it in the upcoming all-out action, 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," the commission said, referring to North Korea by its official name, the Democratic People's Republic of Korea.
U.S. Defence Secretary Leon Panetta said he has seen no outward sign that North Korea will follow through soon on its plan to conduct a test. But that doesn't mean preparations aren't taking place.
"They have the capability, frankly, to conduct these tests in a way that make it very difficult to determine whether or not they are doing it," Panetta told reporters in Washington.
North Korea claims the right to build nuclear weapons as a defence against the United States, its Korean War foe.
Their bitter three-year war ended in a truce, not a peace treaty, in 1953, and left the Korean Peninsula divided by the world's most heavily fortified demilitarized zone. The U.S. leads the U.N. Command that governs the truce and stations more than 28,000 troops in ally South Korea, a presence that North Korea cites as a key reason for its drive to build nuclear weapons.
North Korea is estimated to have stored up enough weaponized plutonium for four to eight bombs, according to scientist Siegfried Hecker, who visited the North's Nyongbyon nuclear complex in 2010.
In October, an unidentified spokesman at the National Defence Commission claimed that the U.S. mainland was within missile range. And at a military parade last April, North Korea showed off what appeared to be an intercontinental ballistic missile.
In 2009, Pyongyang declared that it would begin enriching uranium, which would give North Korea a second way to make atomic weapons.
The National Defence Commission's allusion to a "higher level" nuclear test most likely refers to a device made from highly enriched uranium, said Cheong Seong-chang, an analyst at the private Sejong Institute in South Korea. Experts say North Korea must keep testing its atomic devices so it can make them small enough to mount as nuclear warheads onto long-range missiles.
North Korea tested atomic devices in 2006 and 2009 after receiving U.N. condemnation for launching long-range rockets.
The U.S. envoy on North Korean issues, Glyn Davies, urged Pyongyang not to explode an atomic device.
"Whether North Korea tests or not, it's up to North Korea. We hope they don't do it. We call on them not to do it," he told reporters in Seoul after meeting Thursday with South Korean officials. "It will be a mistake and a missed opportunity if they were to do it."
White House spokesman Jay Carney on Thursday said North Korea's aggressive stance is unnecessary and warned against any further testing.
"North Korea's statement is needlessly provocative and a test would be a significant violation of United Nations Security Council resolutions," he said. "Further provocation would only increase Pyongyang's isolation, and its continued focus on its nuclear and missile program is doing nothing to help the North Korean people."
He said the recent U.N. resolution is a "strong message of the international community's opposition to North Korean provocations and these tightened sanctions will impede the growth of weapons of mass destruction programs in North Korea and the United States will be taking additional steps in that regard."
Carney did not elaborate on what those steps might be.
Despite her firm stand, Park, who takes office next month, wants to leave the window open to constructive dialogue with Pyongyang and will continue to provide food and medical aid as part of a "trust-building" policy for the two Koreas, envoy Rhee said.
"It is a gradual process based on mutual trust and respect, which can begin with keeping promises," he said.
She also advocates returning to the six-nation disarmament negotiations, Rhee said. North Korea walked away from those talks in 2009 and has said future disarmament talks are out off the table.
Associated Press writers Sandy MacIntyre in Davos, Switzerland; Jean H. Lee in Seoul and Matthew Pennington in Washington contributed to this report. Follow AP's Korea bureau chief at www.twitter.com/newsjean.