"We are prepared to stay at the table as long as it is useful," a US embassy spokeswoman said.

The fourth round of talks, which also include China, the two Koreas, Japan and Russia, is scheduled to start on Tuesday although it has not been said when it is due to end. Previous rounds lasted three days.

The chief US negotiator, Undersecretary of State Christopher Hill, is due in Beijing this weekend at the head of a delegation from the State Department, the Pentagon and the National Security Council, the embassy spokeswoman said.

The Stalinist North broke off negotiations in June 2004, rejecting a US offer then on the table which required an up-front pledge to dismantle all its nuclear weapons programs before getting energy and other assistance.

North Korea is seeking a step-by-step formula which would reward incremental efforts at disarmament with aid and which would also result in eventual normalization of ties with the United States.

The standoff began after the United States in late 2002 accused North Korea of operating a covert uranium enrichment program in violation of a 1994 nuclear freeze agreement that was subsequently scuppered.

US President George W. Bush said Tuesday he hoped the new round of talks would result in North Korean leader Kim Jong-Il seeing the "common sense" of abandoning his nuclear weapons drive.

Chinese Foreign Minister Li Zhaoxing said Wednesday China would seek to make the round a "successful and a pleasant one," Xinhua news agency said.

"I am sure all the parties attending the talks will demonstrate mutual understanding and mutual respect, and hold a flexible and practical attitude to promote progress in the talks," he was quoted as saying.

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