The U.S. government believes North Korea will be capable of producing a nuclear bomb using enriched uranium as early as in 2004, Japanese and U.S. sources have told Kyodo News.

The U.S. government made the projection based on the number of centrifugal separators North Korea has imported from Pakistan, the sources said Tuesday. The machines are used to enrich uranium, a process necessary for building bombs.

Sources close to U.S. intelligence said at least 2,000 separators have been shipped to North Korea, countering previous speculation that about 1,000 such machines had been shipped.