North Korea (searchand the United States traded harsh criticism on Thursday, with a U.S. official describing the communist nation as a "hellish nightmare" and the North accusing Washington of "all sorts of lies and plots."

The accusations came amid uncertainty over prospects for a new round of talks on North Korea's suspected development of nuclear weapons, despite South Korean (searchclaims that the process was moving forward.

In Seoul, U.S. Undersecretary of State John Bolton (searchsaid North Korea had not agreed to a U.S. proposal for multilateral talks, and was instead sticking to a demand for one-on-one talks with Washington like a "one-note piano concerto."

"The ball is in North Korea's court," said Bolton, who was in Beijing (search) earlier this week to discuss diplomatic efforts to resolve the standoff. In April, China hosted and participated in contentious talks involving the United States and North Korea.

"The key now is to get South Korea and Japan, and ultimately Russia and others, a seat at the table," Bolton said. "Those with a direct stake in the outcome must be part of the process. On this point, we will not waver."

In remarks likely to infuriate North Korea, Bolton described the country's totalitarian leader, Kim Jong Il, as a "tyrannical dictator" and criticized the North's human rights record and weapons exports.

"While he lives like royalty in Pyongyang, he keeps hundreds of thousands of people locked in prison camps with millions more mired in abject poverty, scrounging the ground for food. For many in North Korea, life is a hellish nightmare," Bolton said.

North Korea, in turn, said the United States should be brought to "international justice" for spreading "misinformation" about Saddam Hussein's weapons of mass destruction before the Iraq war.

Repeating a long-standing accusation, it claimed Washington is building up its forces in South Korea as a prelude to an invasion of North Korea.

"It should also be sternly tried by human conscience for having slandered (North Korea) with all sorts of lies and plots and perpetrated pressure and blackmail against it," Rodong Sinmun, a North Korean newspaper, said Thursday.

Bolton said the United States and its allies were planning "operational training exercises" to prevent the trafficking of missiles and weapons of mass destruction. Impoverished North Korea, which has earned large amounts of hard cash from missile exports, would be a target of the so-called Proliferation Security Initiative.

"The days of (North Korean) blackmail are over. Kim Jong Il is dead wrong to think that developing nuclear weapons will improve his security," Bolton said.

Bolton also said the U.N. Security Council should urge North Korea to drop its suspected development of nuclear weapons and that the council's credibility was at stake.

"Ignoring this issue will not make it go away," Bolton said. "It will only reduce confidence in the Council and suggest to proliferators that they can sell their deadly arsenals with impunity."

Security Council deliberations on North Korea's nuclear threat could eventually lead to U.N. economic sanctions -- which the North has said it would consider a declaration of war. China, North Korea's closest ally and a permanent member of the Security Council, had thwarted previous U.S. attempts to have the council condemn the North over its nuclear ambitions.

South Korea, a U.S. ally, prefers that all other diplomatic options be exhausted before the Council take up the issue.

The nuclear dispute flared in October, when U.S. officials said North Korea admitted having a secret nuclear program in violation of international agreements.