Vice Foreign Minister Wu Dawei was expected to meet Kim Kye-Gwan, the North's chief negotiator to the six-nation disarmament talks, during his visit, 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.

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.

That arrangement would see Pyongyang 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 the communist state 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.