South Korea said Thursday it was preparing for a "worst-case scenario" in North Korea's nuclear standoff with the United States, and a top U.S. envoy warned a resolution of the confrontation would be a "very slow process."

The chief U.N. atomic weapons watchdog, meanwhile, attacked the isolated communist country for engaging in "nuclear blackmail."

South Korean Defense Minister Lee Jun told a parliamentary hearing there was a "high" possibility North Korea would target South Korea if it builds a nuclear bomb. U.S. officials believe the communist regime already has one or two nuclear bombs.

"I believe a war on the Korean Peninsula would be inevitable if the North's nuclear issue could not be resolved peacefully and the United States attacks North Korea," Lee said.

He made the comment while responding to a question by lawmakers over reports that some young South Koreans believe North Korea would not attack South Korea even if it goes to war with the United States.

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 communist regime pulled out of the nuclear nonproliferation treaty last week after the United States suspended oil aid shipments.

Pyongyang insists its confrontation is with the United States, but Lee said South Korea could not escape being swept into a conflict if the standoff spun out of control.

"Our military is preparing for the worst-case scenario," he said.

South Korea's defense chief tends to use hard-line rhetoric to emphasize his military's readiness and his comments Thursday did not indicate Seoul expects the standoff to lead to war.

Traveling in Asia to seek support in getting North Korea to give up its nuclear weapons program, Assistant Secretary of State James Kelly said in Beijing on Thursday there was no quick-fix solution.

Kelly said the international community backs the need for a nuclear-free Korean Peninsula, but it might take a while to achieve that.

"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."

Washington 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.

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."

North Korea lashed out again Thursday in a broadcast by its state-run Central Radio.

"Our military and people are determined to wage a life-or-death fight against U.S. imperialists," South Korea's Yonhap news agency quoted Central Radio as saying.

"We are only awaiting General Kim Jong Il's order to wipe out the enemies," it said.

Meanwhile, the head of the International Atomic Energy Agency criticized North Korea for leveraging atomic weapons in an attempt to resolve its security and energy concerns.

"North Korea should understand that this is no way to proceed for a dialogue through nuclear brinkmanship and nuclear blackmail," Mohammed ElBaradei told a news conference in Moscow. But ElBaradei appeared optimistic about a peaceful end.

"There are elements of a solution to the problem out there," he said.

Elsewhere, diplomatic efforts continued, with U.S., British and French officials meeting in London. They decided on Wednesday that the IAEA's 35-nation board of governors should convene as a next step, a U.S. official said.

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

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

Meanwhile, South Korea pushed forward its own efforts to defuse the tension by setting up Cabinet-level talks with North Korea in Seoul, beginning Tuesday.