The search for a peaceful resolution to the standoff between the United States and North Korea over its nuclear weapons programs will be a "very slow process," a top U.S. envoy to the region said Thursday.

The call for patience from U.S. Assistant Secretary of State James Kelly followed North Korea's angry rejection of American offers to consider energy and agricultural aid to the isolated regime if it gives up its nuclear efforts.

Traveling in Asia to seek support in getting North Korea to give up its nuclear weapons program, Kelly said in Beijing on Thursday that there was no quick-fix solution to the issue and that it would take time to secure a nuclear-free Korean Peninsula.

"And we're going to have to talk and work together and communicate with other people including with North Korea very, very clearly," Kelly said before leaving Beijing for Singapore. "It's going to be a very slow process to make sure that we achieve this in the right way."

Tensions escalated between North Korea and the United States after U.S. diplomats said North Korea admitted in October that it had a secret nuclear program. The isolated communist regime pulled out of the nuclear nonproliferation treaty last week after the United States suspended oil aid shipments.

Washington, however, has taken a more conciliatory stance toward the North in recent days, offering to consider energy, agricultural and other aid to North Korea if the country gives up its nuclear ambitions.

Those offers, however, have not satisfied Pyongyang, which is pushing for a nonaggression pact with the United States and appears to be after more ironclad guarantees of aid before surrendering its nuclear programs.

The state-run news agency KCNA quoted a Foreign Ministry spokesman as saying late Wednesday that the U.S. offers were "loudmouthed" and "pie in the sky." White House spokesman Ari Fleischer called the reported comments "unfortunate."

The South Korean government was also dampened any illusions of a quick solution to the impasse on Thursday.

Defense Minister Lee Jun told a parliamentary hearing that the military was preparing for a "worst-cast scenario" should the standoff between Pyongyang and Washington turn violent.

The comments, which did not include any specifics about the preparations, seemed aimed at dispelling the general complacency about North Korea in the South, where ordinary citizens have shown little sign of alarm.

Lee, for example, said there was a "high" possibility that North Korea would target the South if it builds nuclear weapons. The North has argued that the only confrontation on the peninsula is between Koreans and Americans, not between the North and South.

"We cannot conclude that it (North Korea) would target the Korean peninsula. But we cannot rule out the possibility, and such a possibility is high," Lee said.

On Thursday, the North's news agency said North Korea "wants detente, peace and reunification, not serious tension, confrontation and war."

"If war breaks out in Korea due to the U.S. imperialists keen on nuclear blackmail, it will lead to a nuclear war whose victim will be the Korean nation," it said.

U.S. officials believe the communist regime already has one or two nuclear bombs.

Diplomatic efforts gathered pace, with U.S., British and French officials meeting in London. They decided on Wednesday that the International Atomic Energy Agency's 35-nation board of governors should convene as a next step in the dispute with North Korea, a U.S. official said. Britain's Foreign Office confirmed envoys from the three nations met, but did not say what was discussed.

Two inspectors from the U.N. agency were expelled from North Korea last month, leaving the world without an eye into the secretive nation's nuclear program.

North Korea's Foreign Minister Paek Nam Sun met Maurice Strong, a special adviser to U.N. Secretary-General Kofi Annan, on Thursday, KCNA said. Strong traveled to Pyongyang on Tuesday to try to assess North Korea's needs for foreign food aid.

Also Thursday, North Korea proposed to South Korea that the two sides open talks next Wednesday through Saturday in Pyongyang on connecting cross-border railway and roads.

The Koreas, divided since 1945, have agreed to build two sets of railways and roads across their border. The project, the most visible product of a historic inter-Korean summit in 2000, has suffered delays in recent months amid tensions between North Korea and the United States.

North Korea has indicated that despite the tensions, it wanted to pursue joint projects with South Korea that would bring badly needed cash.

The Koreas are scheduled to hold Cabinet-level talks in Seoul next Tuesday through Friday. South Korea hopes to use the contact to raise its concerns over the nuclear issue.

Both sides also planned to reopen Red Cross talks on reunions for family members separated when the peninsula was divided in 1945. The meetings will take place at the North's Diamond Mountain resort next Monday through Wednesday.