A top US security adviser has claimed the US has already formulated a plan which would see North Korea's nuclear weapons disposed of within a year.

John Bolton, special adviser to the White House on security matters, told CBS's 'Face the Nation' that the US was prepared to move 'very quickly' to dismantle the program if they could ensure North Korean co-operation.

'If they have the strategic decision already made to do that and they're cooperative, we can move very quickly,' Bolton said.

'Physically we would be able to dismantle the overwhelming bulk of their programs within a year.'

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U.S. National security adviser John Bolton said the process could be nearly completed 'within a year'

Donald Trump (right) and Kim Jong-un reached an agreement on denuclearization in Singapore last month

Follow-up talks are scheduled to take place imminently between US secretary of state Mike Pompeo and North Korean officials following a successful meeting between President Trump and Kim Jong-un in Singapore last month.

The Financial Times reported that Pompeo was due to visit North Korea this week but the State Department has not confirmed any travel plans.

Some experts disputed Bolton's optimistic time frame for decommissioning the North's weapons.

'It would be physically possible to dismantle the bulk of North Korea's programs within a year,' said Thomas Countryman, the State Department's top arms control officer under President Barack Obama.

'I do not believe it would be possible to verify full dismantlement within a year, nor have I yet seen evidence of a firm DPRK decision to undertake full dismantlement.'

Last week, 38 North, a website run by the Johns Hopkins University, said satellite imagery showed the North had been upgrading its Yongbyon nuclear complex.

A satellite image published last week shows what is claimed to be ongoing uranium enrichment at a North Korean nuclear facility on June 21

'None of this activity technically violates any agreement Kim may have made,' said Vipin Narang, an associate professor at MIT's security studies Programme.

'What it suggests is that Kim has no intention of surrendering his nuclear weapons.'

Kim agreed at the June 12 summit to 'work toward denuclearisation of the Korean Peninsula,' but the joint statement released after the meeting gave no details on how or when Pyongyang might forsake its nuclear and missile programmes.

Siegfried Hecker, a nuclear scientist and Stanford University professor, has predicted it would take around 10 years to dismantle and clean up a substantial part of North Korea's Yongbyon nuclear site.

Bolton refused to comment on intelligence matters but the United States was going into nuclear negotiations aware of Pyongyang's failure to live up to its promises in the past.

'There's not any starry-eyed feeling among the group doing this,' he said. 'We're well aware of what the North Koreans have done in the past.'