US officials have said they are adjusting their demands in a bid to push ahead in the disarmament process with North Korea, which missed a deadline under a six-nation deal to declare its nuclear programmes by the end of 2007.

"North Korea is the greatest challenge for both Japan and South Korea," Japanese Prime Minister Yasuo Fukuda said after talks with visiting President Lee Myung-Bak.

"We reconfirmed the necessity of demanding that North Korea submit a comprehensive and correct declaration," he said.

Lee, who took over in February, was on his way back from Washington on a maiden trip meant to repair relations with the US and Japan, which were uneasy under his left-leaning predecessor Roh Moo-Hyun.

Ending a decade of liberal rule in Seoul, Lee has pledged to take a harder line on North Korea.

He said he and Fukuda considered North Korea's nuclear programme "a threat not only to the Korean peninsula but to Northeast Asia."

"We exchanged views on how we can resolve the issue peacefully through the six-party process," Lee said.

Kim Sook, Seoul's new pointman in six-nation disarmament talks, said that points in any North Korean declaration "will have to be thoroughly verified one by one."

"The verification will have to be done through objective and scientific proof and examinations, not just listening (to) what North Korea explains. This will take time," he told Seoul-based PBC radio.

North Korea, which in 2006 tested an atom bomb, agreed in a deal last year with China, Japan, Russia, South Korea and the United States to give up its nuclear weapons in exchange for badly needed energy aid and major diplomatic and security benefits.

But the process has been stalled over the communist state's promised nuclear declaration.

A US experts' team led by Sung Kim, director of the Korean Affairs office at the State Department, arrived at Seoul's Incheon airport late Monday en route to the communist North.

Sung Kim told reporters he expects "a very detailed and substantive discussion" in the North about issues related to the declaration.

"We of course hope to have significant progress with this visit," he said, adding that his team would also discuss verifying the document.

"Everything is subject to verification. That is what we need to focus on," Sung Kim added.

Washington says the North Korean declaration should clear up suspicions about North Korea's alleged uranium enrichment and suspected proliferation to Syria. North Korea denies both activities.

According to numerous reports, the North in a face-saving gesture will merely "acknowledge" US concerns about the two issues in a confidential minute to the US side.

Critics, particularly some US conservatives, have argued that the Bush administration was watering down the deal to secure progress before Bush leaves office next January.

US President George W. Bush, meeting on Saturday with Lee, rejected suggestions he was scaling back demands.

"Obviously I am not going to accept a deal that doesn't advance the interests of the region," Bush said.

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