Even as North Korea moves to take back hard-won concessions on its nuclear program, the Bush administration is hoping to salvage a crumbling international effort to get the communist state to give up nuclear arms.

While admitting the situation is dire, especially after Pyongyang took yet another step Monday to restart its atomic reactor, officials say the talks are not dead and have survived troubled fits and starts before.

Over the next week, Secretary of State Condoleezza Rice will meet her counterparts in the negotiations — China, Japan, South Korea and Russia — to discuss possible routes ahead despite North Korea's apparent unwillingness to remain a part of the process.

"The six-party process has had its difficult moments in the past and we're certainly experiencing another one now," said chief U.S. negotiator Christopher Hill. "Clearly, it is a difficult moment ... and it's a time when we're going to have to work together."

"This is a very rough and tumble moment in the negotiation process," he said following an announcement from the U.N. atomic watchdog that North Korea had asked it to remove seals and surveillance equipment from its Yongbyon nuclear reactor.

That step follows the uncrating and reassembling of equipment that had been removed and dismantled in June when the North submitted a long delayed accounting, or declaration, of its nuclear activities as part of the negotiating process.

Since then, amid reports that began to surface in August about the failing health of North Korean leader Kim Jong Il, North Korea has essentially halted cooperation and refused to accept a U.S.-proposed scheme to verify its declaration. This has kept Washington from meeting one of the North's main demands: removal from a U.S. terrorism blacklist.

"They are not ready to reprocess now, but certainly they have taken the machinery out and put it back together," Hill said. "We are concerned about this."

In Washington, State Department spokesman Robert Wood said: "Everyone views this issue with the utmost of concern. ... We want very seriously to bring North Korea back on the path that was outlined."

Hill noted that recent North Korean actions corresponded with the timing of reports about Kim's ill health — "We are seeing a tough line in the last month," he said — but declined to say whether U.S. officials believe the two developments are related.

Instead, he said the U.S. focus was on persuading the North Koreans to reverse their steps to restart Yongbyon and agree to an intrusive verification regime to prove they were telling the truth in their declaration.

"The North Koreans provided a declaration, but unless it is verifiable, we really only have half a loaf here," he said, adding, "We've been able to get through tough spots before."

Hill spoke to reporters after Rice held the first of her North Korea-focused meetings on the sidelines of the annual U.N. General Assembly session with South Korean Foreign Minister Yu Myung Hwan.

She had a private dinner Monday with Chinese Foreign Minister Yang Jiechi, whose country chairs the negotiations and plays a key role in the process. Rice will meet later in the week with the foreign ministers of Russia and Japan.

North Korea said last week it was making "thorough preparations" to start up Yongbyon, which it began disabling last year under a now-stalled disarmament-for-aid deal that took on huge urgency after the country detonated an atomic device in 2006.