VIENNA - North Korea has strong technical reasons to carry out another nuclear test but may be hesitating because it would anger China, a prominent US scientist who has often visited the reclusive Asian state said on Wednesday.
Stanford University's Siegfried Hecker, who was shown a previously undetected uranium enrichment facility when he was last there three years ago, said the North had "everything in place" for what would be the fourth such explosion since 2006.
The impoverished country conducted its third nuclear test in February, prompting stiffer UN sanctions against it.
Like the United States and South Korea, China - North Korea's sole major diplomatic ally - has urged Pyongyang to take steps to end its nuclear programme and to return to dialogue.
Hecker said North Korea "needed additional tests in my opinion to miniaturise", referring to the effort to develop a bomb small and robust enough to fit onto a delivery vehicle such as a missile.
The outside world tries to monitor North Korea's nuclear advances largely via satellite images.
Hecker said the North's tunnel preparations had caused speculation that there could be two tests back in February, but this did not happen and one tunnel remained ready.
"There are strong drivers for them to test again," said Hecker, believed to have been the last Westerner to visit North Korea's Yongbyon nuclear complex. "They have a tunnel that's ready to go if they want to test again," he told a seminar held by an international nuclear-test-ban treaty organisation in Vienna.
But China's displeasure was an important reason "why I think they are hesitating now... The price they have to pay is mostly determined by China", Hecker said.