South Korean President Lee Myung-Bak on Wednesday called for China to play a peace broker role, amid a flurry of diplomacy to revive long-stalled talks on North Korea's nuclear programme.

"I hope China will continue to play an important role in denuclearising the Korean peninsula and leading North Korea to reform and openness," Lee said at talks with Chinese vice premier Li Keqiang.

The meeting came a day after the United States held what were termed "very positive" talks with North Korea in Geneva on restarting the six-party nuclear forum.

Li, widely expected to be China's next premier, had held talks in Pyongyang Monday with North Korean leader Kim Jong-Il, but he did not bring any message from Kim, the president's office said.

Kim reportedly said he wants the six-party talks to resume as soon as possible based on the "principle of simultaneous action" -- a reiteration of the North's stance that the negotiations restart without preconditions.

The president's office quoted Li as saying: "I told Chairman Kim several times that it is important to realise denuclearisation of the Korean peninsula and protect peace and stability."

China hosts the six-party talks, which group it with the two Koreas, Russia, the United States and Japan.

Washington and its allies say Pyongyang must first take action to show its sincerity before restarting the talks, such as shutting down a uranium enrichment plant that could be converted to make nuclear weapons.

Earlier in the day South Korea's nuclear envoy Lim Sung-Nam left for Moscow to meet his Russian counterpart Alexei Borodavkin and other senior officials.

"At this time when two rounds of inter-Korean and North Korea-US meetings have been wrapped up, we will review the progress and discuss future moves," Lim told Yonhap news agency.

The first US-North Korea talks were held in New York in July, followed by the Geneva talks. The two Koreas met in July and September as part of efforts to reopen the multilateral nuclear dialogue.

On Tuesday, Stephen Bosworth, the outgoing US special envoy on North Korea, described the Geneva talks as "very positive and generally constructive" but cautioned that not all differences could be quickly overcome.

North Korea's chief delegate, first vice minister Kim Kye-Gwan, said "big progress" had been made and the two sides had agreed to meet again.

But US State Department spokeswoman Victoria Nuland downplayed the results, saying "while there's been some narrowing of differences, we haven't had any breakthroughs here and significant issues do remain".

The North formally quit the six-party forum in April 2009, a month before staging its second atomic weapons test.