The announcement came as another envoy met Russian ministers in Moscow on a mission to halt the North's suspected nuclear weapons programme, preserve stability on the Korean peninsula and avoid the risk of war with the United States, which has branded the North part of an "axis of evil" along with Iraq and Iran.

Yim Sung-joon, presidential secretary for foreign affairs and security, is to visit Washington from Tuesday to Thursday to meet his counterpart, Condoleezza Rice, and other White House officials.

"In Washington, he will exchange views with US officials on comprehensive ways to resolve the nuclear issue peacefully," presidential spokeswoman Park Sun-sook said. "He will also brief them about our consultations with China and Russia."

Yim is to visit Tokyo on Friday and Saturday.

North Korea, which has thousands of artillery pieces pointed at the South Korean capital, described the standoff as "very serious and unpredictable", chilling words from the KCNA state news agency which usually favours more bombastic rhetoric.

It blamed the United States for the dispute, but said it was still willing to negotiate.

"North Korea has consistently proposed dialogue with the US without preconditions and conclusion of a non-aggression treaty with the US.

"There is no change in the North Korean stand to settle the nuclear issue on the Korean peninsula in a peaceful way."

It said the United States had made "controversial assertions" by saying on the one hand that it would not invade North Korea while refusing to sign a non-aggression treaty.

South Korean Vice Foreign Minister Kim Hang-kyung said in Moscow that South Korea, Japan, China, Russia and the United States had a "common task to solve this problem through peaceful means".

"As you know, Russia stands very strongly for a nuclear-free Korean peninsula and for resolving this issue in a peaceful way, so in that sense we are in agreement", he said on his way into talks with officials at the foreign ministry on Sunday.

"I will discuss this issue with my counterpart today."

He is believed to be pushing a three-point plan in which poverty-stricken North Korea is guaranteed security and fuel oil in return for an end to any nuclear weapons programme.

"To be realistic, it's not going to be easy," said Dong Yong-seung, a North Korea specialist at Samsung Economic Research Institute.

"North Korea and the United States view the issue from completely different angles."

For South Korean President Kim Dae-jung and president-elect Roh, who swept to power on a wave of passionate anti-American sentiment, Pyongyang's brinksmanship presents the task of coordinating diplomatic efforts involving the United States, China, Russia, Japan and, most recently, France.

"We all have a common task to solve this problem through peaceful means," Seoul's special envoy to Moscow said.

Another South Korean delegation is due to present Seoul's latest proposals at talks in Washington on Monday with the United States and Japan ahead of a visit to Seoul by US Assistant Secretary of State James Kelly next week.

Japanese Foreign Minister Yoriko Kawaguchi and US Secretary of State Colin Powell agreed in telephone talks late on Saturday to continue using diplomacy to press North Korea over nuclear and other issues, Japan's Kyodo news agency reported.

Washington cut off oil supplies to North Korea after Pyongyang told a US official in October it had a covert nuclear programme.

North Korea then kicked out UN atomic energy inspectors monitoring a nuclear complex mothballed under a 1994 deal in which Pyongyang had agreed to end such work in exchange for fuel oil from the United States and its allies.

North Korea restarted a reactor at the complex, saying it was acting in self-defence but that it was still willing to talk to Washington and the International Atomic Energy Agency.

It said a non-aggression pact with the United States was the only way to defuse the crisis but Washington has refused to bite.

An IAEA source said the agency would likely suggest giving North Korea another chance to co-operate and allow inspectors back in before it takes the matter to the UN Security Council. The IAEA meets on Monday.

Dong, of the Samsung Economic Research Institute, said that for North Korea, nuclear development was literally an act of self-defence, guarding its communist system against external military threats.

"But the United States wants to deal with the North as a country proliferating weapons of mass destruction," he said. "For them, guaranteeing the North's security is one thing, while its nuclear arms programme is quite another."

- REUTERS