Vice foreign minister Wu Dawei was met by North Korean officials and representatives from the Chinese embassy, the North's official Korean Central News Agency said in a brief dispatch.

It gave no further details but South Korea's Yonhap news agency said Wu would stay in the North until Thursday.

Wu's trip came as concerns arise over whether North Korea will declare and disable all its nuclear programmes by year-end, as agreed.

Under a six-nation pact the North must disable its plutonium-producing plants and declare all nuclear programmes and facilities, in return for major energy aid.

But the process has reportedly hit a key problem -- the North's refusal to address its suspected highly enriched uranium (HEU) weapons programme to US satisfaction.

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 he reiterated the demand after Kim gave a "verbal reply" to what was an unprecedented letter from Bush.

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 US accused North Korea of having a secret HEU weapons programme in addition to its declared plutonium operation. Pyongyang has never admitted having such a programme.

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

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

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