WASHINGTON, Jan 21: North Korea is accumulating plutonium that could be used to make a nuclear weapon from a reactor that has been restarted at its controversial Yongbyon research complex, a top US atomic expert said on Wednesday.

But Pyongyang has denied it has a highly enriched uranium programme that could enable the faster production of nuclear weapons, according to Siegfried Hecker, an atomic expert who was part of an unofficial US delegation that went to Yongbyon this month.

He said in comments prepared for an address to the US Congress that a small experimental reactor at the complex was working again after North Korea ended a freeze on its nuclear development.

"The five-megawatt reactor has been restarted; it appears to be operating smoothly, providing heat and electricity, also accumulating approximately six kilograms of plutonium per year in its spent fuel rods," said Hecker, a senior fellow at the Los Alamos National Laboratory in New Mexico.

Hecker confirmed that the spent fuel pond at Yongbyon is now empty. "The approximately 8,000 fuel rods have been moved," he said. The fuel rods were estimated to contain between 25 and 30 kilograms of plutonium. "We could not definitively substantiate that claim," said Mr Hecker.

But he said laboratory staff had showed "the requisite facility, equipment and technical expertise and they appear to have the capacity" to extract the plutonium.

US intelligence experts believe that stock could provide Pyongyang with the ingredients for up to six nuclear bombs. The Central Intelligence Agency says North Korea may already have one or two crude atomic weapons.

North Korean Vice Minister Kim Gye Gwan rejected international suspicions about the North Korean nuclear programme during talks with Jack Pritchard, Hecker said. Pritchard was until recently the US envoy on North Korea.-AFP