Seoul: North Korea on Friday brought down a cooling tower at its Soviet-era nuclear plant, said South Korean broadcaster MBC, which has a crew at the site.

The 18-metre cooling tower at North Korea's main nuclear power plant collapsed in a heap of shattered concrete and twisted steel.

The demolition was filmed by international and regional television broadcasters invited to witness the event.

It was part of a process of dismantling the state's nuclear programme in return for easing its international isolation.

"As you all saw, the cooling tower is no longer there," Sung Kim, a senior US State Department official, told South Korean television. "It's a very significant disablement step."

Pyongyang on Thursday handed over an account of its nuclear programme, fulfilling a key requirement in six-nation talks on halting North Korea's nuclear weapons programme.