Washington had earlier told Tokyo that Pyongyang already possessed small nuclear warheads that could be mounted in ballistic missiles, the Nihon Keizai Shimbun said.

The Rodong has an estimated range of 1,300 kilometres (800 miles), which makes it capable of hitting anywhere in Japan.

South Korea's Yonhap news agency reported Sunday that North Korea had told the United States it had completed reprocessing spent fuel rods to extract plutonium for nuclear weapons.

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