A U.S. envoy called Wednesday for international condemnation of North Korea over its shelling of a South Korean island, a day after he ruled out resuming six-nation nuclear disarmament talks with the North while it works on a new uranium facility.

Washington's reluctance to resume the talks is at odds with China's position, which is keen to get back to discussions as soon as possible.

Stephen Bosworth has been conducting hurried consultations with North Korea's neighbors, including China, after a U.S. nuclear scientist reported visiting a new sophisticated uranium enrichment plant that could improve North Korea's ability to make and deliver nuclear weapons.

The situation was made more critical after North Korea on Tuesday shelled a populated South Korean island and the South returned fire.

"The United States calls upon the DPRK (Democratic People's Republic of Korea) to cease its provocative and irresponsible actions against its neighbors and fully abide by the terms of the armistice and adhere to its international obligations," Bosworth told reporters at a Beijing hotel. "We call on all members of the international community to condemn the DPRK's acts and make clear that they expect the DPRK to cease all provocations and implement its denuclearization commitments."

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The appeal for a strong reaction was clearly directed at China, North Korea's economic and political benefactor. Beijing's public reaction has been extremely cautious so far, with a Foreign Ministry spokesman expressing concern over the situation and calling on both the North and South to "do more to contribute to peace and stability on the peninsula."

On Tuesday in Tokyo, Bosworth said that North Korea's work on the new facility makes it impossible to resume negotiations on its nuclear disarmament that stalled last year.

"Needless to say, we regard this development with great seriousness," Bosworth told reporters at a Tokyo hotel. "We do not contemplate resuming negotiations while active programs are under way or while there is a possibility that North Koreans will test another nuclear device or test a missile."

A Chinese Foreign Ministry spokesman, however, said the report of the new nuclear installation made an early resumption of talks more necessary.

"We have taken note of the relevant report" on the facility, said the spokesman, Hong Lei. "What is imperative now is to restart six-party talks as soon as possible."

Disagreements between the U.S. and China over how best to coax Pyongyang to the table have occasionally roiled the talks, which also involve, Japan, Russia and South Korea as well as North Korea. Pyongyang had agreed to dismantle its nuclear programs in return for aid and other concessions before the talks foundered last year after North Korea conducted a second nuclear test.

Cooperation between Beijing and Washington is considered key, though, to any progress on the nuclear issue. After talking with the Chinese foreign minister, Bosworth made an apparent nod to that cooperation.

"We strongly believe that a multilateral, diplomatic approach is the only way to realistically resolve these problems," he said.

Despite North Korea's moves, Beijing worries more about instability in its communist neighbor, preferring to offer aid, trade and other incentives as a way to encourage Pyongyang's cooperation.

The new North Korean uranium facility, which Stanford University scientist Siegfried Hecker over the weekend reported that he was taken to, is part of the main Yongbyon atomic complex. Hecker reported that the facility appeared modern and that his North Korean hosts told him that it contained 2,000 centrifuges to enrich uranium.

The North's previously known nuclear program is plutonium-based. At low levels, uranium can be used in power reactors, but at higher levels it can be used in nuclear weapons.