North Korea "is not quite ready to be giving us a complete listing of all their programmes, all their facilities and all their nuclear materials. So that is the key issue," Hill told reporters here after a trip to Japan.

The communist country should have disabled its key nuclear facilities by December 31 and given a full declaration of its nuclear programmes under a deal a year ago with China, Japan, South Korea, Russia and the US.

But it missed the deadline. A North Korean foreign ministry statement last week said that Pyongyang was near to completing the disabling and gave a full account to Washington in November -- a claim Washington denied.

"I'm not too concerned about being a little late. The main concern is when they do give a declaration, we want it to be complete," Hill said.

Washington says it has evidence that Pyongyang has imported material for a suspected uranium enrichment programme along with plutonium-based activities. North Koreans have never admitted any uranium operation.

"They have not wanted to list programmes we know about," Hill said while refusing to go into specific details.

The North has slowed compliance with the six-party deal, accusing the other parties of failing to deliver promised aid and said Washington had yet to remove Pyongyang from its list of state sponsors of terrorism.

North Korea has so far received about 150,000 tonnes of heavy fuel oil and 5,000 tonnes of steel as an alternative form of aid, according to Seoul.

"The disablement has gone well. I know they (North Koreans) talk about slowing down, but frankly a lot of actions have been completed," Hill said.

Seoul's foreign ministry said Hill would meet with his South Korean counterpart Chun Yung-Woo late Tuesday and other ministry officials Wednesday.

On Thursday, Hill will meet South Korea's president-elect Lee Myung-Bak, who has signalled a tougher line on the North than the outgoing Roh Moo-Hyun.

Lee has urged the North to fully scrap its nuclear weapons programmes in return for major economic aid from Seoul. He takes office next month.

"We would look forward to having a very close relationship with the next government," Hill said, stressing the need for a strong US-South Korea alliance to resolve the nuclear issue.

Hill, who also called for a "100 percent declaration" from North Korea at Monday's talks with his Japanese counterpart Kenichiro Sasae in Tokyo, said a full account was crucial to moving on to end its nuclear ambitions.

Under a proposed final phase of the deal, the North is to dismantle its plants and hand over all nuclear materials in return for diplomatic relations with the US and Japan and a formal peace treaty on the Korean peninsula.

After Seoul, Hill is to head for talks in China and Russia. He said he would hold talks with Chinese officials on setting the next date of the six-party talks.