BEIJING, Feb 28: Six-party talks on the North Korean nuclear crisis ended on Saturday without a breakthrough but a senior US official said the meetings had advanced Washington's agenda of disarming Pyongyang.

Chinese Foreign Minister Li Zhaoxing closed the four-day session saying all sides had agreed to set up a working group and hold the next set of talks in Beijing before the end of June.

"Differences, even serious differences, still exist," Li said at the closing ceremony, without specifying what gaps remained.

China's chief negotiator, Wang Yi, cited an "extreme lack of trust" between the US and North Korean side and said further discussions were needed on the scope of both the North's proposal to freeze its nuclear programmes and the US demand for dismantling all atomic arms schemes.

But a senior US official declared the talks that also involved South Korea, Japan and Russia "very successful", saying all but Pyongyang had agreed to the goal of a nuclear-free North.

"The event has exceeded my expectations in a very important respect. It's been very successful in moving the agenda towards our goal of complete, verifiable and irreversible dismantling (CVID) of DPRK nuclear programmes," the US official said. "CVID is now more on the table than ever."

Russia's chief delegate, Alexander Losyukov, said the talks achieved "modest" results. But he called the working groups "a reasonable base for the continuation of discussions of those problems arising from the different positions".

Analysts said, however, that Washington and Pyongyang could both dig in their heels in this US presidential election year.

"North Korea does not have to strike any agreement now, ahead of the November election in the United States," said Yu Suk-ryul of Seoul's Institute of Foreign Affairs and National Security.

"The United States has a need to avoid collapse of the talks before the election," he said.

China's Li said the second round featured substantial dialogue and made "a big step forward".

"The road is longer and more bumpy. But time is on our side. Time is on the side of peace," Li said.

But there was little evidence the gulf between North Korea and the United States had narrowed. In the end they settled on a chairman's summary statement instead of a joint declaration.

"They (the Americans) haven't succeeded, but they haven't failed and they can always say that the process is under way," said Peter Hayes, director of the Nautilus Institute in Berkeley.

North Korea, whose 11th-hour rejection of language in a proposed agreement prolonged the talks for hours and prevented the parties from signing a joint declaration, repeated its denial that it had an enriched uranium weapons programme.

"We believe the insistence of the raising of the HEU (highly enriched uranium) issue by the US side is very much related to the position of the US Bush administration, who based this assertion on false information," Kim Gye-gwan, head of the North Korean delegation, told reporters after the talks.

Kim also repeated North Korea's denial that it had acquired uranium enriching know-how from Pakistan, despite a confession this month by Islamabad's top nuclear scientist, Dr Abdul Qadeer Khan, that he had sold nuclear secrets to Pyongyang.

The crux of the dispute and the reason for the six-party talks is a US accusation - which North Korea denies - that North Korea is pursuing a uranium enriching programme for bombs.

Asked about the North's offer to give up its military nuclear programme but not its peaceful one, the official said: "The problem is, I am not aware of any peaceful programmes in the DPRK".-Reuters