The United States has a plan that would lead to the dismantling of North Korea's nuclear weapons and ballistic missile programmes in a year, National Security Adviser John Bolton has said.

Mr Bolton told CBS' Face the Nation that Washington has devised a program to dismantle North Korea's weapons of mass destruction - chemical, biological and nuclear - and ballistic missile programmes, 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,” Mr Bolton said. “Physically we would be able to dismantle the overwhelming bulk of their programmes within a year.”

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

Meanwhile, Donald Trump told Fox News that he believes North Korean leader Kim Jong-un is sincere, but a deal may not happen.

“I made a deal with him, I shook hands with him, I really believe he means it,” the president said in an interview aired on Sunday. “Now, is it possible? Have I been in deals, have you been in things where, people didn’t work out? It’s possible.”

North Korea Military Parade Show all 6 1 /6 North Korea Military Parade North Korea Military Parade In this image made from video released by KRT on Feb. 8, 2018, a military parade is held at Kim Il Sung Square in Pyongyang, Thursday, Feb. 8 2018, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade This screen grab taken from North Korea's KCTV on February 8, 2018 shows members of North Korea's military taking part in a parade, with missiles being displayed, in Kim Il Sung Square in Pyongyang. North Korea staged a military parade in Pyongyang on February 8 to mark the 70th anniversary of its armed forces, in a show of strength just a day before the Pyeongchang 2018 Winter Olympic Games open in the South. / AFP PHOTO / KCTV / KCTV / -----EDITORS NOTE --- RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / KCTV" - NO MARKETING - NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS - NO ARCHIVESKCTV/AFP/Getty Images AFP/Getty Images North Korea Military Parade In this image made from video released by KRT, North Korean soldiers march during a military parade in Pyongyang, Thursday, Feb. 8 2018. North Korea held a military parade and rally on Kim Il Sung Square on Thursday, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade In this image made from video released by KRT on Feb. 8, 2018, North Korean leader Kim Jong Un, right, inspects honor guards, along with his wife Ri Sol Ju, center, during a military parade in Pyongyang, Thursday, Feb. 8 2018. North Korea held a military parade and rally on Kim Il Sung Square on Thursday, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade In this image made from video released by KRT on Feb. 8, 2018, North Korean leader Kim Jong Un, center, watches the military parade in Pyongyang, Thursday, Feb. 8 2018. North Korea held a military parade and rally on Kim Il Sung Square on Thursday, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade This screen grab taken from North Korea's KCTV on February 8, 2018 shows North Korean leader Kim Jong Un speaking during a military parade in Kim Il Sung Square in Pyongyang. North Korea staged a military parade in Pyongyang on February 8 to mark the 70th anniversary of its armed forces, in a show of strength just a day before the Pyeongchang 2018 Winter Olympic Games open in the South. / AFP PHOTO / KCTV / KCTV / -----EDITORS NOTE --- RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / KCTV" - NO MARKETING - NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS - NO ARCHIVESKCTV/AFP/Getty Images AFP/Getty Images

Some experts dispute Mr Bolton's optimistic time frame. “It would be physically possible to dismantle the bulk of North Koreaâ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... 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.

Trump says media coverage of his North Korea summit 'almost treasonous'

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 Mr 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.

North Korea agreed at the summit to “work towards denuclearisation of the Korean Peninsula,” but the joint statement signed by Kim Jong-un and Mr Trump in June 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

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, according to The Washington Post. It also reported Pyongyang has secret production facilities, according to the latest evidence they have.

Mr 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 programmes 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.”

Republican Senator Susan Collins said she was troubled by the news reports. “North Korea has a long history of cheating on agreements that itâs made with previous administrations,” she said on CNN's State of the Union. Ms Collins stressed the need for “verifiable, unimpeded, reliable inspections” of the North's weapons programmes.

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.