"From the current attitudes of the parties involved, there are major difficulties in the attempt to hold the meeting as scheduled," foreign ministry spokesman Kong Quan said at a regular briefing.

He blamed the "serious confrontation" and "the lack of trust" between North Korea and the United States for the impasse but said China had not given up hope that a solution could be found.

"It is a bumpy road, there have always been difficulties during the process but we have already overcome many problems and have made a lot of progress," he said.

"We're worried but we won't abandon our efforts to push all parties to display pragmatism, restraint and flexibility in their efforts."

The last round of talks in Beijing, which also include South Korea, Japan and Russia, failed to make any clear progress other than an agreement to meet again by the end of September.

But North Korea has since hardened its position. It says the talks cannot resume unless nuclear experiments by South Korea are clarified and Washington changes its hostile policy.

The nuclear stand-off flared in October 2002 when the United States accused North Korea of operating a nuclear weapons programme based on enriched uranium in violation of a 1994 agreement.

Pyongyang has denied running the uranium-based program but has restarted its plutonium program.

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