Think tank: N. Korea's plutonium enough for nukes

North Korea has enough plutonium to build an estimated four to eight crude nuclear warheads that could potentially be mounted on medium-range missiles, a Washington-based think tank said. The Institute for Science and International Security said in a report released Tuesday that as of this month, North Korea had between 46 and 64 kilograms (101 and 141 pounds) of plutonium, of which between 28 and 50 kilograms (62 and 110 pounds) is estimated to be usable for weapons. The amount of radioactive material in the communist nation is key to monitoring its compliance with a February 13 agreement to disarm, under which the North is required to declare all nuclear programs and material to international inspectors.