"It is unfortunate that this declaration has not been provided yet," the foreign ministry's press secretary Mitsuo Sakaba said in a statement.

"North Korea needs to provide a complete and correct declaration of all its nuclear programmes as quickly as possible," he added.

Japan also urged the communist state to "steadily carry out, and complete at an early date, disablement of the three nuclear facilities at Yongbyon," he said.

Pyongyang, which tested an atom bomb last year, was given until the end of 2007 to disable and declare all its nuclear programmes in the next stage of a six-nation aid-for-disarmament deal reached earlier this year.

North Korea has gone ahead with disablement of its plutonium-producing Yongbyon reactor, the most visible symbol of its nuclear drive.

But the declaration has proved difficult, with South Korea indicating the obstacle was over whether Pyongyang was ready to disclose a suspected uranium enrichment programme.

In the meantime, North Korea has informed the United States it is reducing the shifts of workers carrying out disablement steps at its nuclear facilities, Japan's Kyodo News reported Monday out of Beijing, quoting unnamed diplomats.

Pyongyang has told Washington it is cutting from four shifts to one shift a day the work of North Koreans overseen by US nuclear experts, the news agency said.

North Korea reportedly said last week it may slow down work to disable its nuclear plants because of what it called a delay in promised energy aid.

Japan has been the most critical member of the six-nation talks, sometimes putting itself at odds with the United States, its main ally.

Japan has tense relations with North Korea, in part due to the regime's kidnappings of Japanese civilians in the 1970s and 1980s to train its spies.