VIENNA - North Korea would need to carry out at least one more atomic test in order to develop a nuclear missile, a prominent US scientist who has often visited the isolated Asian state said on Thursday.
Stanford University's Siegfried Hecker, who in 2010 was shown a previously undetected uranium enrichment facility in North Korea, said he believed it might be able to conduct its fourth such explosion soon, in weeks or months.
The North has threatened nuclear attacks on the United States, South Korea and Japan after new UN sanctions were imposed in response to its latest nuclear arms test in February.
"My view is that they need at least one more nuclear test and most likely several more nuclear tests," said Hecker, who is believed to have been the last Westerner to visit North Korea's Yongbyon nuclear complex.
"It is primarily in order to be able to miniaturize (a bomb to fit on a missile) and have sufficient confidence that you can put a nuclear weapon on a warhead," he told reporters during a visit to Vienna.