North Korea has bought a complete nuclear weapon from either Pakistan or a former Soviet Union state, a South Korean newspaper has reported. The newspaper Seoul Shinmun quoted an unnamed source as saying the United States was checking the intelligence. North Korea is believed to have at least one or two nuclear weapons. US Congressman Curt Weldon said after a visit to North Korea this month that its second ranked leader had told his delegation that it possessed nuclear weapons.Pyongyang has previously declared that a nuclear reactor at Yongbyon, sealed under a 1994 agreement with the United States, has been restarted. Spent nuclear fuel from that reactor could be converted to weapons-grade material. North Korea has never officially declared that it possessed atomic weapons, speaking instead of its nuclear deterrent. US experts who visited the Yongbyon facility said spent plutonium previously stored there had been removed. North Korea is suspected of running a separate program based on uranium enrichment technology, assisted by a former top Pakistani nuclear scientist.