North Korea has promised to abandon all nuclear weapons and programmes in exchange for economic and diplomatic incentives in a 2005 agreement between the two Koreas, China, Japan, Russia and the United States.

However, the deal has been stymied by Pyongyang's failure to meet an end-2007 deadline to disclose its nuclear programmes.

A senior U.S. official said Rice hoped her Asian trip would act as "a real catalyst to get over this bar of a good declaration" and she particularly wanted help from China, the North's major trading partner and traditional Communist ally.

"We continue to believe that if anyone is capable of convincing the North that this kind of transparency is the only way forward, it's the Chinese," said the official, who spoke anonymously because of the sensitivity of the diplomacy.

According to U.S. officials and analysts, the sticking point has been Pyongyang's reluctance to discuss any nuclear technology it may have transferred to other nations, notably Syria, as well as its suspected pursuit of uranium enrichment.

The United States has questions about any possible North Korean role in a suspected Syrian covert nuclear site that was bombed by Israel in September. Syria has denied having a nuclear programme but the case remains murky.

INAUGURATION

Rice, who attended South Korean President Lee Myung-bak's inauguration in Seoul on Monday, arrived in Beijing on Tuesday and flies to Tokyo on Wednesday.

She has no plans to visit Pyongyang, where the New York Philharmonic orchestra will play a concert featuring the works of Antonin Dvorak and George Gershwin on Tuesday.

In Beijing, Rice was due to meet Chinese President Hu Jintao, Premier Wen Jiabao and Foreign Minister Yang Jiechi.

The talks are likely to touch on efforts to get a third U.N. Security Council resolution passed imposing sanctions on Iran for its nuclear programme, as well as on human rights, an issue in focus ahead of this year's Olympic Games in Beijing,

Rice also plans to discuss how the six nations that reached the agreement on ending North Korea's nuclear ambitions might monitor it, including tracking whether North Korea proliferates nuclear technology in the future.

The Bush administration has championed a "Proliferation Security Initiative" (PSI), which organised countries in a voluntary but controversial programme to share intelligence and interdict trade in weapons of mass destruction.

Charles "Jack" Pritchard, a former U.S. negotiator with North Korea, said that by expanding the six-party process to cover such issues Washington hoped to "formalise discussion about what North Korea is up to regarding proliferation without having to twist arms to get the (others) to join PSI".

Japan, Russia and the United States are all members of PSI while China, South Korea and North Korea -- one of the prime targets of the effort -- are not.

"I am less certain that North Korea will agree. It comes close to institutionalising Pyongyang as a permanent defendant in the court of six-party talks," Pritchard said.