WASHINGTON • US National Security Adviser John Bolton said yesterday that he believed the bulk of North Korea's weapons programmes could be dismantled within a year, although some experts say the complete process could take far longer.

Mr Bolton told CBS' 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 programmes 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 programmes 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 Mr Pompeo was due to visit North Korea this week, but the State Department has not confirmed any travel plans.

Dr Siegfried Hecker, a nuclear scientist and Stanford University professor, visited the heart of North Korea's nuclear programme in Yongbyon in 2010. He predicted it would take around 10 years to dismantle and clean up a substantial part of that site.

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

US intelligence is not certain how many nuclear warheads North Korea has.

The Defence 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 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.

Meanwhile, Mr Kim has appealed to Chinese President Xi Jinping to help end sanctions against the North, a Japanese newspaper reported yesterday, citing multiple unnamed sources in the two countries.

Mr Kim made the request during his third meeting with Mr Xi in Beijing last month, and the Chinese leader promised to do his "utmost" to satisfy it, the Yomiuri Shimbun newspaper said.

"We are feeling great pain due to economic sanctions. Now that we have concluded the US-North Korea summit in success, I want (China) to work towards early lifting of the sanctions," Mr Kim reportedly told Mr Xi, according to the newspaper.

In recent months, Cold War-era allies China and North Korea have sought to repair ties strained by Pyongyang's nuclear tests and Beijing's support of subsequent United Nations sanctions.

Mr Kim chose Beijing - his main economic patron and diplomatic protector - for his first official foreign trip in March and met Mr Xi again in May in the north-eastern port city of Dalian.

Japanese broadcaster NHK reported that China's UN mission and its Russian counterpart last Thursday submitted to the UN Security Council a draft press statement calling for the easing of sanctions on the North.

Mr Kim's third official visit to China just days after the Trump-Kim summit was seen as a move to reassure Beijing that Pyongyang would not neglect its interests after the historic summit with Mr Trump in Singapore.

China and the US both hope to see the Korean peninsula free of nuclear weapons. But Beijing is concerned Washington and Pyongyang might move closer at its expense, a possibility that China sees as threatening to its economic and security interests in the region.

AGENCE FRANCE-PRESSE, REUTERS