The communist state has told the United States "through indirect channels" that it had resumed construction of a 50,000-kilowatt reactor in Yongbyon and a 200,000-kilowatt one in Thaechon, said the evening edition of the Nihon Keizai Shimbun.

It cited US government and other sources.

Fresh building work has been confirmed through spy satellite photographs and other data, the sources told the business daily.

The reactors are suitable for extracting plutonium, a material essential to the building of nuclear bombs, the newspaper said, adding that the North Korean move is apparently intended to speed up nuclear weapons production.

Completion of the graphite-moderated reactor facilities is expected to take several years, it said.

The top Japanese government spokesman said Tokyo had yet to confirm the information.

"We are not sure about the actual situation and intentions behind the (reported) move," Chief Cabinet Secretary Hiroyuki Hosoda told a regular press conference.

"North Korea can produce a good amount of plutonium at the existing facility," he said, apparently referring to a reactor at Yongbyon.

It is uncertain whether Pyongyang is considering using the facilities reportedly under construction "for power generation or production of nuclear weapons," Hosoda said.

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