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 state said yesterday.

Stanford University's Siegfried Hecker, who was shown a previously undetected uranium enrichment facility on a visit three years ago, said the North had "everything in place" for the fourth such explosion since 2006.

The impoverished country conducted its third nuclear test in February, prompting stiffer UN sanctions.

Like the US and South Korea, China has urged Pyongyang to take steps to end its nuclear programme and to return to dialogue.

Hecker said the North's tunnel preparations had caused speculation that there could be two tests back in February, but this did not happen.

"There are strong drivers for them to test again," said Hecker, adding 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.