John Bolton, US undersecretary of state for arms control and international security, said there was little reason for optimism after discussions with Chinese vice foreign minister Zhang Yesui.

"Am I any more optimistic, no. I'm not any more pessimistic either. I don't know if I've learnt anything that affects my optimism scale one way or the other," he said after day-long discussions on the nine-month-old standoff.

He said China, North Korea's closest ally, had done all it could to facilitate a resumption of talks.

"I'm not sure that there's anything else specifically that we could think of that the government here could do that they haven't already tried," said Bolton, in Beijing en route to South Korea and Japan.

"That's not the question, the question is whether and when North Korea is going to take the steps necessary to dismantle its nuclear weapons program."

Asked if progress had been made on setting a date for a resumption of talks following a first round of trilateral discussions in April, he replied: "I don't think there is anything on a date one way or the other that I could really indicate."

In Seoul, South Korea's foreign minister also poured cold water on any early resumption of dialogue after a recent spate of shuttle diplomacy that has seen a Chinese envoy go to Pyongyang and then Washington.

"At the beginning I believed it was possible to resume the talks at an early date," Yoon Young-Kwan told South Korean journalists.

"But as time passes, the North Korean-Chinese consultation is slowing down, rather than speeding up. We need to wait."

China hosted trilateral talks with the United States and North Korea in Beijing in April, but they were widely seen as a failure.

According to US accounts, North Korea said it possessed nuclear weapons, and threatened to sell or even use them.

Recently, Beijing has intensified efforts to broker a second round amid claims from Pyongyang that it has reprocessed enough spent fuel roads for several atomic devices.

Only last week, South Korean National Security Advisor Ra Jong-Yil said he believed that talks could take place in August while the Russian foreign ministry said they would likely be in early September.

However, Chinese Foreign Minister Li Zhaoxing, at a meeting of foreign ministers from Europe and Asia in Bali last week, hinted at obstacles when he said the US and North Korea needed to be more flexible.

The United States favours a multilateral format while Pyongyang has insisted on one-on-one talks, although a compromise agreement that would see trilateral talks expanded to multilateral are believed to be on the table.

Washington has made clear South Korea and Japan must be involved and Bolton Monday insisted that Moscow should also be included, even suggesting the talks be thrown open to a wider audience.

"It's been our view that Russia should participate in multilateral discussions about the North Korean nuclear weapons program," he said at a press conference.

"In fact, we think that it would be useful for all five of the legitimate nuclear weapons states to participate."

The crisis flared last October when Washington said Pyongyang had admitted having a secret nuclear program in violation of a 1994 bilateral accord, and suspended fuel deliveries to the energy-starved state.

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