North Korea is disabling its plutonium-producing reactor and other plants under a six-nation deal reached in Beijing last year with the US, China, Japan, Russia and South Korea.

But disputes over the declaration due at the end of last year have blocked the start of the final phase of the process - the permanent dismantling of the plants and the handover of all material.

Under the terms of the deal, in return for total denuclearisation North Korea is due to receive energy aid, a lifting of US sanctions, the establishment of diplomatic relations with Washington and a formal peace treaty ending the Korean War.

North Korea's declaration has been held up partly because of Pyongyang's reluctance to discuss allegations of any transfer of nuclear technology to other countries, notably Syria.

The US says North Korea has helped Syria with a suspected nuclear reactor project that Israel destroyed in an air strike last September.

It also has accused Pyongyang of pursuing a uranium enrichment program, which could provide it with a second way to produce fissile material for nuclear weapons in addition to the plutonium-based program used in its 2006 nuclear test.

However, in an effort to revive the deal the US has indicated in recent weeks that it is willing to soften its stance on the North Korean declaration.

Under a face-saving compromise, the declaration is expected to be split in two parts with North Korea giving a detailed disclosure of its plutonium program on the one hand, while on the other providing an "acknowledgment" of US concerns about its suspected uranium enrichment and proliferation activities on the other.

Earlier this month North Korea handed over copies of 18,822 pages of documents on its plutonium program to a visiting US envoy.