A global crackdown on North Korea's nuclear weapons programme began today, with countries divided over how to enforce UN sanctions in a foreboding sign that imposing the punitive measures may not be easy.

RESULTS from an initial air sampling after North Korea’s announced nuclear test showed no evidence of radioactive particles that would be expected from a successful nuclear detonation, a US government intelligence official said last night.

The chief US envoy to talks on North Korea’s nuclear programme said today delegates would start work on a joint statement of principles, taking the negotiations into a “new stage”, but he said progress was slow and there was unlikely to be any agreement this weekend.