The move fed fears about a resurgent nuclear North Korea, but there also is speculation it might be motivated by negotiating strategy. Pyongyang could use the year needed to restart its sole reprocessing plant to wrest more concessions from the U.S. and others seeking to end the atomic program.

Still, coming amid reports leader Kim Jong Il suffered a stroke, the nuclear reversal is raising nervousness about a breakdown in the international attempt to coax the North out of its confrontational isolation — a point addressed Wednesday by Secretary of State Condoleezza Rice.

U.S. diplomats are talking with other nations involved in bargaining with the North at this week's meeting of the U.N. General Assembly.

Any move by Pyongyang to restart its nuclear program "would only deepen its isolation," Rice warned. "We strongly urge the North to reconsider these steps and come back immediately into compliance with its obligations" under a disarmament-for-aid agreement reached in six-nation talks.

Hours earlier, the International Atomic Energy Agency announced that North Korean officials "informed the IAEA inspectors that they plan to introduce nuclear material to the reprocessing plant in one week's time."

David Albright, a nuclear expert with the Institute for Science and International Security, said restarting the reprocessor could take longer if North Korea wants to run tests.

"It's a plant that handles a lot of liquids. They are reattaching a lot of equipment. They have to make sure they reattached them correctly and did the welds," Albright said.

It could be accomplished more quickly if North Korea is willing to be less careful about leaks.

"It could happen as soon as next week," he said.

The statement from the Vienna-based U.N. agency said Deputy IAEA Director General Olli Heinonen told the IAEA board that after a request from North Korea, his inspectors removed all agency seals and surveillance equipment from the reprocessing plant and its immediate area.

That work "was completed today," Heinonen said, according to the statement.

It also said North Korea barred IAEA inspectors from further access to the Yongbyon nuclear complex.

North Korea had signaled in recent days that it would break out of the disarmament deal, announcing it was making "thorough preparations" to restart Yongbyon.

"What they've done is trouble," said Gregory L. Schulte, the chief U.S. delegate to the IAEA. South Korean Prime Minister Han Seung-soo called the North's actions "very unfortunate" and "very regrettable" and urged patience in dealing with the country.

But their comments were measured, reflecting concerns that harsh condemnation could backfire by accelerating the North's move to restore its nuclear operations.

North Korea's recent moves have deepened the guessing game about leadership in Pyongyang, where Kim is reportedly ill and possibly incapacitated.

"There is uncertainty about who is in charge, or if some sort of transition is in the process of taking place with the military, who have probably not been too happy to give up their (nuclear) trump card," said Robert S. Norris, senior research associate at the Natural Resources Defense Council in Washington.

"Now that he may be weakened — or who knows, dead — there may be emerging ... a possible clique of hard-liners who may want to play hardball again," he added.