The International Atomic Energy Agency said North Korea can have no peaceful use for the plutonium its Yongbyon nuclear reactor will produce, if it goes ahead with plans to activate the facility.
Mohamed ElBaradei, the chief of the agency, issued a statement on Thursday accusing the North Koreans of "nuclear brinksmanship". Later, he told the Cable News Network the situation in North Korea is very worrying, particularly because his agency has little ability to monitor what is happening there.
North Korea has disabled electronic monitoring equipment.
The agency has sent a substitute inspector to the site to relieve one of the two permanently based there. The agency's spokesman Mark Gwozdecky said they are doing the rounds but it is a very large facility.
Mr. Gwozdecky said the North Koreans continue to move fresh fuel rods into the Yongbyon reactor. The complex has a capacity of 8,000 fuel rods, and by Thursday the IAEA said 1,000 rods had been delivered. The North Koreans have told the agency they need one to two months to make the reactor operational.
Mr. Gwozdcky said the main source of concern for the IAEA is the plant's ability to reprocess and store plutonium.
"The reprocessing plant is where they extract the plutonium and this is the stuff of nuclear weapons," he said. "Without our measures in place we are not in a position to monitor that facility and therefore we cannot know whether this material is used for peaceful purposes or for weapons. Frankly, the big question is that they have no peaceful use for plutonium in North Korea at the moment. There are certain countries where you can use plutonium and have fuel but they do not have the fuel cycle to support that."
The IAEA has called a special meeting of its board of directors for the first week in January, in Vienna.
The board can refer the matter to the U.N. Security Council if the North Koreans continue to be uncooperative.
The 35 member body includes the United States, Russia, Japan and Iran, and is currently chaired by Kuwait.