North Korea has "good technical reasons" to carry out at least one more atomic test if it wants to develop a nuclear-armed missile, a prominent U.S. scientist who has often visited the reclusive Asian state said on Friday.
The North tested nuclear devices in 2006 and 2009, but still has not shown it has a working nuclear bomb.
Proliferation experts have said the country has enough fissile material for up to 10 nuclear weapons, but they don't believe it can miniaturise one to place on a missile.
Stanford University's Siegfried Hecker, who late last year was shown a previously undetected uranium enrichment facility in North Korea, said he believed the isolated state knew how to build a "relatively simple, rudimentary plutonium bomb".
But, "I don't believe they could have confidence on the basis of those tests to make one small enough to mount on a missile," Hecker told a seminar for diplomats in Vienna.
"So if they want ... to have the confidence that they had one they can mount on a missile, if they want to convince the rest of the world, they would need at least one other nuclear test."
In October last year, a South Korean government source was quoted as saying that a U.S. satellite had detected increased activity at a North Korean nuclear weapons test site, suggesting it could be preparing for a third test. Read More