North Korea has insisted that funds frozen as part of a US-led crackdown must be released before any progress can be made on nuclear disarmament, underlining the challenges facing diplomats as they prepare for the resumption of talks on Pyongyang’s nuclear ambitions next week.

Two days of talks this week in Beijing between US and North Korean officials over the financial crackdown were “very productive”, the top American delegate said. But there was no indication that any legally earned funds frozen during the crackdown would be returned, as some had expected.