South Korea ? North Korea said that 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 the communist country, 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.