North Korea has restarted its nuclear facilities to harvest weapons-grade plutonium, an official said Saturday, in an escalation of the communist state's standoff with the international community over its nuclear and missile programs. The announcement came hours after a UN Security Council committee approved new sanctions on three major North Korean companies in response to Pyongyang's April 5 rocket launch. "The reprocessing of spent fuel rods from the pilot atomic power plant began," the North Korean Foreign Ministry spokesman said in comments carried by the North's official Korean Central News Agency. The move "will contribute to bolstering the nuclear deterrence for self-defense in every way to cope with the increasing military threats from the hostile forces." North Korea - which carried out a nuclear test in 2006 - is believed to have enough weaponized plutonium to build half a dozen bombs. Pyongyang has expelled international nuclear monitors, vowed to restart its atomic program and quit disarmament negotiations to protest a previous UN Security Council condemnation of its rocket launch. The North says the rebuke was unfair because the rocket was carrying a satellite. But the US and others believe it was a test of long-range missile technology. The new sanctions approved Friday require nations that have dealings with the three North Korean companies to freeze their assets. The committee actions are final and do not require additional approval. The companies are Korea Mining Development Trading Corp. and Korea Ryongbong General Corp., both of which were previously sanctioned for suspected involvement in ballistic missile transactions, and Tanchon Commercial Bank, which managed the transaction funds. Pak Tok Hun, deputy chief of North Korea's diplomatic mission to the UN in New York, reacted angrily, saying Pyongyang will not accept any decision from the Security Council, according to South Korea's Yonhap news agency. "The peaceful use of space is a right which cannot be deprived of any country," Yonhap quoted him as saying. "The recent activity of the UN Security Council shows that we cannot expect anything from it unless it is democratized." South Korea's Foreign Ministry said it would come up with measures to implement the UN decision, but it said it has no immediate comment on the North's announcement. Russian Foreign Minister Sergey Lavrov on Friday renewed his country's opposition to sanctions against North Korea over the launch and called for efforts to revive the stalled talks on ending Pyongyang's nuclear programs. "Sanctions are not constructive," he said in a news conference with his South Korean counterpart. Lavrov flew to Seoul after his two-day trip to Pyongyang failed to persuade North Korean officials to end their boycott of the nuclear negotiations. He called on the countries involved in the disarmament talks to create conditions necessary for resumption of the discussions. The six nations - China, Japan, the two Koreas, the US and Russia - should "honor their obligations," Lavrov said. South Korean President Lee Myung-bak met Lavrov on Saturday, but no details of the meeting were immediately available. Under a 2007 deal, North Korea agreed to dismantle its atomic program in exchange for much-needed aid and other concessions. That process has been stalled since last July over a dispute with Washington over how to verify its past atomic activities.