The US has long suspected that Pyongyang had this kind of nuclear program.
If the statement is true, it means the North Koreans will have developed a backup means of producing the fissile material that lies at the heart of atomic weapons.
And it is a backup that is easy to hide. Production of plutonium – North Korea's primary fissile material – requires huge nuclear reactors. In contrast, enriched uranium is produced by arrays of narrow spinning tubes, called centrifuges.
An enriched-uranium program "can be done in small unidentifiable facilities, no larger than a warehouse, which are difficult to identify," said Victor Cha, a North Korea expert at the Center for Strategic and International Studies (CSIS), on Friday.
In a letter to the United Nations Thursday, North Korea said that it has almost completed reprocessing into plutonium thousands of spent fuel rods from its Yongbyon nuclear reactor. This fissile material will be used for weapons, said the letter.
In addition, the letter said, North Korean scientists have successfully carried out uranium-enrichment tests. "That process is in the concluding stage," said the letter, which was published by North Korean official media.