A US scientist who visited a secret North Korean nuclear site last year says Pyongyang may seek to launch a third atomic test to enable it to develop a small fissile warhead that can be carried by a missile.
Siegfried Hecker who first revealed news of a previously clandestine North Korean uranium enrichment plant also expanded on details of that facility on Friday.
He said it was more advanced than Iran's enrichment operation, and could be re-engineered to turn out enough fissile material to make two nuclear weapons a year.
The North tested nuclear devices in 2006 and 2009 based on plutonium like enriched uranium, a potential source of fissile warhead material.
North Korea dismantled or mothballed much of its plutonium producing capacity several years ago as part of now shattered commitments to denuclearise in exchange for economic and political concessions from the US and other global or regional powers. Before that, however, the North amassed enough plutonium for up to seven bombs.
At a lecture today, Hecker said Pyongyang remains committed to having a nuclear deterrent and may want to launch a test at least one more time to progress from developing a small and sophisticated missile warhead from the basic weapon it now has. "The second test was a necessity because the first one didn't work well," Hecker said.
While the North now has the knowledge to make "a rudimentary plutonium bomb ... they would need one more nuclear test" to develop a modern missile warhead, he said.
Hecker said that the North has appeared to shut down its plutonium production for good after dismantling its Yongybon reactor and mothballing other facilities four years ago, but expressed concern about the enrichment programme that he revealed last year.