"We would be able to resume our verification activities at short notice, within weeks, not months", International Atomic Energy Agency (IAEA) Director General Yukiya Amano told reporters at a press conference.

Amano's comments come as preparations continue for next week's historic summit between US President Donald Trump and North Korean leader Kim Jong Un in Singapore.

"We have liaised with stakeholders and had a number of exchanges" on the issue, he added.

"It is very clear that if there is anybody, any organisation that can do the verification, it is only us," Amano went on.

He said it was difficult to predict the size of any possible inspection operation, but that the agency would be able to mobilise many staff to take part if needed.

In 2009 Pyongyang expelled IAEA inspectors from its Yongbyon nuclear site and has since refused to allow IAEA inspections on its territory.

The Singapore summit will be the first time a sitting US president has met a North Korean leader.

Talks are expected to focus on denuclearisation of the Korean peninsula and improving relations between Washington and Pyongyang.

The main stumbling block is likely to be the concept of "denuclearisation" itself -- both sides say they are in favour of it, but there is a yawning gap between their definitions.

On Sunday US Defence Secretary James Mattis said North Korea would not get any sanctions relief until it demonstrated "irreversible" steps to denuclearisation.