Vice Foreign Minister Wu Dawei was also to meet North Korean leaders, including top nuclear envoy Kim Kye-Gwan, during his visit that began Tuesday, ministry spokesman Qin Gang told journalists.

"The purpose of his visit is to exchange ideas with the DPRK (North Korean) side... on the current situation in the six-party talks and the work for the next phase," Qin said, without saying how long Wu would stay in Pyongyang.

"We believe that the six-party talks have made positive progress and that the good momentum should be maintained and pushed forward."

Xinhua news agency said Wu inspected the disablement process at the Yongbyon atomic power plant, while North Korea's state media said the Chinese envoy had also met with North Korean Foreign Minister Pak Ui-Chun.

Qin refused to discuss recent concerns over whether North Korea would declare and disable all of its nuclear programmes by the end of this month, as agreed in a six-nation pact, but said all sides should make efforts for more progress.

"Relevant parties should overcome difficulties, deepen mutual trust and cooperation so as to implement the (denuclearisation) agreement in a comprehensive way," Qin said.

The six-party pact calls on Pyongyang to disable its plutonium-producing plants and declare all nuclear programmes and facilities by December 31, in return for energy aid and the promise of future major diplomatic concessions.

But the process has reportedly hit a key problem -- the North's refusal to address its suspected highly enriched uranium weapons programme to the satisfaction of the United States.

US President George W. Bush this month wrote to North Korean leader Kim Jong-Il, urging him to fully disclose his country's nuclear programmes.

On Friday Bush reiterated the demand after Kim gave what US officials said was a "verbal reply" to the unprecedented letter.

Bush called for a full declaration of "programmes, materials that may have been developed to create weapons, as well as the proliferation activities of the regime".

The latest nuclear crisis began in late 2002, when the United States accused North Korea of having a secret highly enriched uranium weapons programme in addition to its declared plutonium operation.

Pyongyang has never publicly admitted having a highly enriched uranium programme.

The crisis escalated last year when North Korea tested a nuclear bomb.

The six-party talks group the two Koreas, host China, the United States, Russia and Japan.