The London-based International Institute for Strategic Studies issued its findings in a 120-page report.

It says solid and confirmable intelligence on North Korea's nuclear program is virtually impossible to acquire, and no firm conclusions can be drawn.

But institute director John Chipman said North Korea could be on the brink of a major increase in nuclear weapons production.

"In a worst case," said Mr. Chipman, "if the facilities are completed in the next one or two years, North Korea's output of nuclear weapons could significantly increase around mid-decade to about eight to 13 weapons every year."

Mr. Chipman says he leans toward a more conservative analysis, that it could take North Korea until the end of this decade to finish a new reactor and a uranium-enrichment plant needed to step up bomb production.

He says that no matter which scenario comes true, there is a lot of pressure on diplomatic negotiations. "This analysis suggests that there is still some time for diplomatic efforts to halt and eliminate North Korea's nuclear arsenal while it remains limited to a handful of nuclear weapons," he said. "As time elapses, however, a diplomatic solution could become more difficult as Pyongyang acquires additional strategic bargaining chips."

The report says that since the early 1990s North Korea has acquired enough plutonium to build a few nuclear weapons even if questions remain about whether it has done so.