North Korea plans to blow up the cooling tower at its Yongbyon atomic complex to symbolise its commitment to nuclear disarmament, a senior South Korean official said Wednesday.

The tower will be toppled soon after the communist state hands over a long-awaited declaration of its nuclear activities, Seoul's chief nuclear negotiator Kim Sook told reporters.

"It will come on the heels of the declaration," he said at Incheon airport on his return from talks in Washington with his US and Japanese counterparts.

Kim was answering questions about widespread media reports that the tower would be destroyed in a symbolic gesture.

He said he expected six-party negotiations on the next steps in the disarmament process to resume in the first half of next month.