"It is unfortunate that North Korea has not yet met its commitments by providing a complete and correct declaration of its nuclear programs and slowing down the process of disablement," said State Department spokesman Tom Casey in a statement.

The United States, he added, will continue to work with Japan, South Korea, China and Russia "as we urge North Korea to deliver a complete and correct declaration of all its nuclear weapons programs," under an October agreement.

"The United States is committed to fulfilling our obligations under the Six Party agreements as North Korea fulfills all its obligations," Casey said.

Under the six-nation pact, North Korea is required to disable its main nuclear plants by December 31 and declare all its nuclear programs and weaponry. In exchange, the six parties agreed to cooperate in economic and energy assistance to North Korea.

Failing full disclosure from the Stalinist state, the United States will look to other unspecified options, State Department spokesman Rob McInturff told AFP earlier Sunday.

"Right up until the deadline we are still hoping to see full disclosure from the North Koreans," he said.

"If that doesn't happen by midnight (on Monday), we'll reevaluate and look to other options," McInturff said.

Experts have said the US-supervised disablement is going well, but may not be completed by year-end for technical reasons related to the removal of fuel rods used to make potentially weapons-grade uranium.

However, South Korean officials have said the North is unwilling to give what the United States considers a satisfactory explanation of a suspected highly enriched uranium weapons programme.

China, Japan and South Korea have all said that Pyongyang is likely to miss the deadline. US officials have said they are ready to wait a short while for a full and complete declaration from North Korea.

US allegations of a secret highly enriched uranium programme, in addition to North Korea's declared plutonium operation, led to the breakdown in 2002 of the last nuclear pact.

In October 2006, the North staged an atomic test but then agreed to return to six-party talks, where it was agreed that in exchange for making its plants unusable and declaring all nuclear activity, the energy-starved North should receive a million tons of energy aid or its equivalent.

South Korea has already made a shipment of 5,100 tons of steel plates to the North, apparently for use in patching up its decrepit power stations.

Japan has refused to contribute any aid until a row over Japanese citizens abducted by the North is settled.

North Korean, South Korean and Chinese officials held talks last week in Pyongyang aimed at agreeing the type of aid China was to supply under the next step in the deal.

Under a final phase next year, North Korea would dismantle its plants and hand over all nuclear materials in return for diplomatic relations with the United States and Japan, an end to sanctions and a formal peace pact on the Korean peninsula.