US has plan to dismantle North Korea nuclear programme within a year: John Bolton

White House national security adviser John Bolton said on Sunday he believed the bulk of North Korea's weapons programs could be dismantled within a year, although some experts say the complete process could take far longer.

Bolton told CBS's "Face the Nation" that Washington has devised a programme to dismantle North Korea's weapons of mass destruction - chemical, biological and nuclear - and ballistic missile programs in a year, if there is full cooperation and disclosure from Pyongyang.

"If they have the strategic decision already made to do that and they're cooperative, we can move very quickly," he said. "Physically we would be able to dismantle the overwhelming bulk of their programs within a year."

He said Secretary of State Mike Pompeo will likely discuss that proposal with the North Koreans soon. 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.

"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."

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.

South Korea media reported on Sunday that US envoy Sung Kim, the American ambassador to the Philippines, met with North Korean officials at the border on Sunday to coordinate an agenda for Pompeo's next visit to North Korea.

US intelligence is not certain how many nuclear warheads North Korea has. The Defense Intelligence Agency is at the high end with an estimate of about 50, but all the agencies believe Pyongyang is concealing an unknown number, especially smaller tactical ones, in caves and other underground facilities around the country.

TRUST BUT VERIFY

North Korea agreed at the summit to "work toward denuclearisation of the Korean Peninsula," but the joint statement signed by North Korean leader Kim Jong-un and US President Donald Trump on June 12 gave no details on how or when Pyongyang might surrender its nuclear weapons.

US intelligence agencies believe North Korea has increased production of fuel for nuclear weapons at multiple secret sites in recent months and may try to hide these while seeking concessions in nuclear talks with the United States, NBC News quoted US officials as saying on Friday.

The Washington Post reported on Saturday that US intelligence officials have concluded that North Korea does not intend to fully give up its nuclear arsenal and is considering ways to hide the number of weapons it has. It also reported Pyongyang has secret production facilities, according to the latest evidence they have.

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.

"We know exactly what the risks are - them using negotiations to drag out the length of time they have to continue their nuclear, chemical, biological weapons programs and ballistic missiles," he said.

"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."

Asia expert Patrick Cronin called the NBC and Washington Post reports "extremely worrisome."

Cronin, senior director of the Asia-Pacific Security Program at the Center for a New American Security, said he had heard from US and South Korea officials that Pompeo was expected to return to Pyongyang at the end of this week and that Sung Kim was working to prepare the way for that trip.

The US side was "working to see whether they can prepare for high-level talks between Secretary Pompeo and Kim Jong Un and others in Pyongyang that would be a specific denuclearisation road map, or at least significant dismantlement steps that could fill in a roadmap," he said.

Republican Senator Susan Collins said she was troubled by the news reports. "North Korea has a long history of cheating on agreements that it's made with previous dministrations," she said on CNN's "State of the Union." Collins stressed the need for "verifiable, unimpeded, reliable inspections" of the North's weapons programs.

Another of Trump's fellow Republicans in the US Senate, Lindsey Graham, echoed the need for scepticism.

"If it is true that they are saying one thing and doing another, nobody should be surprised," he said on NBC's "Meet the Press."