North Korea threatened Wednesday to conduct nuclear and missile tests unless the UN apologizes for criticizing its April 5 rocket launch, dramatically raising its stake in the worsening standoff over its atomic programs. Pyongyang's Foreign Ministry said in a statement the country "will be compelled to take additional self-defensive measures" unless the UN Security Council apologizes immediately. "The measures will include nuclear tests and test-firings of intercontinental ballistic missiles." North Korea is known for brinksmanship and harsh rhetoric, but it is unusual for it to threaten a nuclear test. The country conducted its first-ever atomic test blast in 2006. The UN Council adopted a statement earlier this month denouncing the North's rocket launch and calling for tightening sanctions. Pyongyang has claimed the rebuke is unfair because the liftoff was a peaceful satellite launch. But the US and others believe it was a test of long-range missile technology. Wednesday's threat came days after the North said it had begun reprocessing spent nuclear fuel rods at its Yongbyon nuclear complex - a move aimed at harvesting weapons-grade plutonium. That announcement came hours after the UN blacklisted three North Korean companies. The Security Council should apologize for infringing on the North's sovereignty "withdraw all its unreasonable and discriminative resolutions and decisions" against the North, the ministry said in a statement carried by the official Korean Central News Agency. Professor Kim Yong-hyun at Seoul's Dongguk University said the North's threat "appears to be rhetoric for now." "The North is trying to maximize the stakes as the United States keeps ignoring it," he said. But the expert also said the communist could gradually put the threat into action depending on reaction from Washington. The North's ministry also said the country will build a light-water nuclear reactor and start developing technologies to produce nuclear fuel, a threat that Kim said means that it would start enriching uranium - another type of nuclear bomb ingredient. Under a 2007 six-nation deal, North Korea agreed to disable its main nuclear complex in Yongbyon north of Pyongyang in return for 1 million tons of fuel oil and other concessions. In June 2008, North Korea blew up the cooling tower there in a dramatic show of its commitment to denuclearization. But disablement came to halt a month later as Pyongyang wrangled with Washington over how to verify its past atomic activities. The latest round of talks, in December, failed to push the process forward. The negotiations involve China, Japan, the two Koreas, Russia and the US.