Top nuclear negotiator Chun Yung-Woo, marking the first anniversary of the landmark aid-for-disarmament accord, put a positive spin on the process which is currently deadlocked.

"It is now nearly impossible for North Korea to produce additional plutonium for the time-being," Chun told a briefing.

Eight of 11 measures which the North promised to take to disable its nuclear facilities have been completed, he added, saying it would take more than a year to reactivate the plants when disablement is completed.

The North staged a nuclear test in October 2006 but later agreed to return to six-party negotiations grouping the two Koreas, the United States, China, Russia and Japan.

A landmark deal reached on February 13, 2007 offers the North a million tons of fuel oil or equivalent energy aid, normalised relations with the United States and Japan and a formal peace treaty, if it scraps all nuclear programmes and material.

In the current phase the North agreed to disable its atomic plants and fully declare all nuclear programmes by the end of last year. But it missed the deadline amid a dispute with the US over the declaration.

Pyongyang says it submitted a list in November. But the US says it must account fully for a suspected secret UEP (uranium enrichment programme), which the North has consistently denied having.

"It is undoubtedly North Korea that should be responsible for presenting evidence to clarify the UEP," Chun said. "It is a daunting task but not an issue that is impossible to settle."

The South Korean envoy did not expect the declaration issue to derail the six-nation process, but reiterated a call for the North to give a "complete and correct" declaration to keep the process afloat.

The envoy warned against any prolonged deadlock. "We will not be able to let the current situation go on indefinitely like this," Chun said.

In Japan, which has tense ties with North Korea, Chief Cabinet Secretary Nobutaka Machimura urged Pyongyang to keep to its promises.

"Frankly speaking, things haven't moved as we had originally designed," the top government spokesman told a news conference.

"It is regrettable that there is a delay because the North Korean side has failed to complete procedures as they promised," he said. "We expect a more positive response in future from the North Korean government."

North Korean official media say Pyongyang has slowed down the disarmament work in response to what it sees as the failure of negotiating partners to keep their side of the agreement.

In particular, it wants the US to start the process of removing it from a list of state sponsors of terrorism. Washington says this depends on receiving a full declaration.

Asked if the North was really willing to give up all its nuclear material, Chun said it was premature to judge. "We have to wait and see."

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