The newly-appointed US envoy to six-nation talks on the North Korean nuclear problem, Christopher Hill, and South Korea's chief negotiator, Deputy Foreign Minister Song Min-Soon, both arrived from Seoul.

The visits come one week after North Korea declared publicly that it now possessed nuclear weapons and would no longer take part in the talks.

The discussions in Beijing also come ahead of an expected weekend visit to Pyongyang by a special envoy from China, the broker and host of the six-nation talks and North Korea's closest ally.

"I'm here to meet my Chinese counterpart," Hill said before heading into meetings with China's pointman on North Korea Wu Dawei.

Hill, the US ambassador to South Korea, was appointed to his new role on Monday to replace the retiring James Kelly.

The US embassy said he would use the trip as a "familiarisation process, but obviously the North Korean nuclear talks will top his agenda." Hill is due to return Seoul later Thursday.

The United States, Japan and South Korea -- who along with Russia are the participants in the six-nation dialogue -- believe China's influence over the unpredictable regime is crucial to bringing back to the negotiating table.

"South Korea and the United States have agreed that China's role is crucial," South Korean Foreign Minister Ban Ki-Moon told reporters Wednesday on his return from talks with US counterpart Condoleezza Rice in Washington.

Wang Jiarui, the head of the Chinese Communist Party's International Liaison Department, will visit Pyongyang "soon" to discuss "international and regional issues where both sides are concerned," his office told AFP.

It is widely believed he will leave on Saturday.

The flurry of diplomacy follows telephone discussions between most of the key players, including between the foreign ministers of Russia and North Korea.

Both sides Wednesday "spoke out in favor of a rapid resumption of the six-way negotiating process", the Russian foreign ministry said in a statement.

The last round of six-party talks took place in Beijing in June last year.

North Korea shunned a fourth round set for last September, complaining of "hostile" US policies.

The United States and North Korea have been locked in a stand-off since October 2002 when Washington accused Pyongyang of operating a secret program based on highly-enriched uranium, violating a 1994 arms control agreement.

North Korea denied the allegations. However it responded by expelling UN nuclear inspectors, re-starting a mothballed nuclear reactor and extracting weapons-grade plutonium from spent fuel rods.

The hectic diplomacy came as the United States said North Korea also has active biological and chemical weapons programs and could resume missile tests soon.

"North Korea could resume flight testing at any time ... including longer range missiles capable of reaching the United States," CIA Director Porter Goss testified at a Senate Intelligence Committee hearing in Washington.

"We believe North Korea has active CW (chemical weapons) and BW (biological weapons) programs ... ready for use."

Goss did not say whether North Korea's nuclear technology would allow it to launch a nuclear-tipped missile.

In 1998, North Korea launched a long-range ballistic test missile over key US ally Japan, becoming one of Tokyo's biggest security worries and prompting Japan to begin researching missile defence.

In a phone conversation with Chinese counterpart Li Zhaoxing, Japanese Foreign Minister Nobutaka Machimura Wednesday made clear Tokyo would not tolerate a nuclear-armed North Korea.