China's top negotiator on the North Korean nuclear issue arrived in Pyongyang on Monday, the North's official news agency reported.

The one-sentence report gave no details of the visit by Wu Dawei, China's chief negotiator at long-stalled six-nation talks aimed at ending North Korea's nuclear programme.

The talks grouping the forum host China, the two Koreas, the United States, Japan and Russia have not been held since December 2008.

South Korea's Yonhap news agency said Wu's visit appeared to be another attempt by Beijing to restart the dialogue.

Wu visited Washington late last month to meet his US counterpart and other officials dealing with North Korea policy.

China is North Korea's sole major ally and key economic benefactor, but has grown increasingly frustrated with its pursuit of a nuclear deterrent.

Following Pyongyang's third nuclear test in February, Beijing agreed to a tightening of UN sanctions already in force.

The North has expressed interest in principle in returning to the six-party talks, but has repeatedly said it has no intention of abandoning its atomic weapons programme.

South Korea's spy agency confirmed last month that the North has restarted an ageing plutonium-producing reactor that could help boost the programme.