SEOUL North Korea said on Tuesday it had completed reprocessing spent fuel rods at its Yongbyon nuclear plant and turned it into arms-grade plutonium, giving the mercurial state more material to produce atomic arms.
The announcement comes after the reclusive North, hit with fresh U.N. sanctions to punish it for a nuclear test in May, has warmed up to the outside world in recent months and indicated it could return to stalled international nuclear talks.
"We have finished reprocessing 8,000 spent fuel rods as of August. We have made substantial achievements in weaponising plutonium from the extraction," KCNA said.
Experts said the North might be able to produce enough material for at least one more atomic weapon from the spent fuel rods at its Soviet-era Yongbyon plant, which was being taken apart under a sputtering, six-way disarmament-for-aid deal.
The North already had enough fissile material for about six to eight nuclear weapons, experts said.
"They (North Korea) are just telling us that they are biding their time and increasing pressure on the United States ahead of bilateral talks," said Yang Moo-jin, a professor at the South's University of North Korean Studies.
The North called on Monday for direct talks with its long-time foe, the United States, and gave the clearest signal so far it was ready to return to nuclear disarmament talks it has boycotted for almost a year.
That followed last week's rare visit by a North Korean official to the United States and what has been a "charm" offensive by the ostracised state that some analysts say is looking increasingly desperate for finance and aid.
The sanctions following the nuclear test were aimed at cutting off the cash the North receives from its arms sales. Some estimates say those account for more than $1 billion (613 million pound) a year in a state with a $17 billion annual economy.
"The sanctions caused the North to drop its hard-line policy but we have not seen any indications yet that Pyongyang has made a strategic decision to change its nuclear arms policy," said a diplomatic source in Seoul.
While North Korea would have to make concessions in the nuclear dealings if it wanted aid, few analysts think leader Kim Jong-il would ever give up his nuclear programme, seen at home as the crowing achievement in his military-first rule that has also prevented a U.S. invasion.
North Korea said in April it had started extracting fuel rods from its ageing Yongbyon nuclear plant, a few weeks after the country was hit with separate U.N. punishment for a long-range rocket launch viewed as a disguised missile test that violated U.N. resolutions.
The Yongbyon plant also houses an ageing reactor and a plant that makes fuel to burn in the reactor. Those facilities and the reprocessing centre were being taken apart under the nuclear deal among the two Koreas, China, Japan, Russia and the United States.
South Korean government sources said there have been no indications yet the North has been rebuilding the reactor and fuel plant, which would signal it plans to restart all of Yongbyon, capable of producing about one bomb's worth of fissile material when fully operational, experts said.
North Korea said in June it had started a programme to enrich uranium, which could give it a second path towards making an atomic bomb.
(Additional reporting by Christine Kim; Editing by Jonathan Thatcher and Jerry Norton)