SEOUL, South Korea (AP) – North Korea said Saturday it has begun harvesting plutonium from spent fuel rods at its main nuclear plant to build up its atomic arsenal. The move, in defiance of tightening U.N. sanctions, threatened to further damage efforts to dismantle the communist nation’s rogue program.

“This will contribute to bolstering the nuclear deterrence for self-defense in every way to cope with the increasing military threats from hostile forces,” the official Korean Central News Agency quoted a North Korean Foreign Ministry spokesman as saying Saturday.

North Korea carried out a nuclear test in 2006 and is thought to have enough weaponized plutonium to make more than half a dozen atomic bombs. Five nations – Russia, China, South Korea, Japan and the U.S. – have been negotiating for years on disarming it, but North Korea has walked away from the talks.

Saturday’s announcement, which could not be independently verified, came just hours after the U.N. imposed new sanctions on three North Korean companies in response to the country’s controversial April 5 rocket launch.

North Korea says it sent a satellite into orbit as part of a peaceful bid to develop its space program. The U.N. Security Council called the rocket launch a violation of resolutions barring the North from missile-related activity, since the delivery systems for satellites and missiles are similar.

North Korea retaliated by quitting the disarmament talks and vowing to restart its atomic facilities. Last week, Pyongyang expelled international nuclear monitors from the main nuclear site at Yongbyon, north of the capital.

With eight of 11 steps toward disablement complete at Yongbyon, outside experts have said it could take months for the North to get the plant fully restarted.

Kim Yong-hyun, a professor at Seoul’s Dongguk University, called the newest move a bluff designed to pressure Washington into holding direct talks with Pyongyang outside of the six-party process.

Kim predicted the North will take further provocative steps as long as the U.S. continues to ignore it.

The disablement process culminated in the dramatic destruction of a cooling tower in June 2008. But the process halted weeks later because of a dispute with Washington over how to verify North Korea’s past nuclear activities.

The latest round of talks in December failed to end the deadlock.

The new U.N. sanctions require nations that have dealings with three North Korean companies – the Korea Mining Development Trading Corp., Korea Ryongbong General Corp., and Tanchon Commercial Bank – to freeze their assets.

The deputy chief of North Korea’s diplomatic mission to the U.N., Pak Tok Hun, rejected the decision.

Russian Foreign Minister Sergey Lavrov, who made little progress during a visit to North Korea on Thursday, assured South Korean President Lee Myung-bak in Seoul on Saturday that Moscow would continue trying to draw Pyongyang to the negotiating table, Lee’s office said.

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