BEIJING: Top US and South Korean diplomats were in Beijing for meetings with Chinese officials on Wednesday as part of the latest efforts to nudge North Korea back to stalled nuclear disarmament talks.

China, host of the six-party talks and the communist North's only major ally, has said the future of the on-off talks depended on the willingness of Washington and Pyongyang to work together.

The talks began in 2003 and have been on hold since the North stormed out 10 months ago.

Washington's special North Korea envoy Stephen Bosworth was to discuss the disarmament issue with Chinese Vice Foreign Minister Wu Dawei in Beijing later on Wednesday, Chinese and US officials said.

South Korean chief negotiator Wi Sung-Lac also met Wu as part of a two-day visit that began on Tuesday.

South Korea's Yonhap news agency quoted Wi saying his talk with Wu was "constructive" but that the future remained unclear.

"We need to watch further," he was quoted saying, adding it remained uncertain how the various discussions would turn out.

The Chinese deputy minister briefed Wi about North Korea's preconditions for a return to the six-nation forum as outlined by its chief nuclear negotiator Kim Kye-Gwan during a visit to Beijing two weeks ago.

Bosworth, who was travelling with US chief nuclear negotiator Sung Kim, was due to visit Seoul -- where he will meet Wi -- and Tokyo after his stop in Beijing.

Media reports have said the North is insisting on two conditions for returning to dialogue: the lifting of UN sanctions and a US commitment to discuss a formal peace treaty on the Korean peninsula.

The United States, South Korea and Japan say the North must first return to dialogue and show it is serious about denuclearisation.

Under deals in 2005 and 2007 the North agreed to scrap its nuclear weapons in return for aid and major diplomatic and security benefits, including a formal peace pact.

But the talks became bogged down by disputes over ways to verify disarmament and in April last year the North quit them altogether.

On Tuesday, a senior North Korean Communist Party official, Kim Yong-Il, met his Chinese counterpart Wang Jiarui and President Hu Jintao.

The North Korean official discussed the nuclear issue and delivered a message from leader Kim Jong-Il to Hu, the China Daily reported.

Pyongyang, which tested atomic weapons in October 2006 and May 2009, says it developed nuclear weaponry because of a US threat of aggression, and it must have a peace pact before it considers giving them up.

The 1950-1953 Korean War ended only in an armistice. Seoul officials suspect talk of a peace treaty is an excuse to delay action on the nuclear programme.