Beijing - US and Chinese officials on Saturday discussed the latest setback in the six-nation process to end North Korea's nuclear weapons programme, after a US envoy said his key concern was the verification mechanism for the dismantling of the programme.

US Assistant Secretary of State Christopher Hill met China's chief envoy in the nuclear talks, Wu Dawei, and said his South Korean and Japanese counterparts also planned to meet Wu in Beijing on Saturday.

Hill said late Friday that North Korea had indicated concerns about how the disablement and dismantlement of its nuclear facilities would be verified.

"They are very clear they have concerns about the verification protocol," Hill told reporters.

"And I think we've made equally clear, as have the other members of the six-party process, that part of the declaration is to have a verification protocol," he said.

Hill said he had no plans to meet North Korean officials in Beijing, but added that the United States was "certainly prepared to sit down in six-party meetings again or directly with the North Koreans to hear their concerns about the (verification) protocol".

He met the South Korean and Japanese envoys on Friday, amid uncertainty over whether Pyongyang is preparing to reassemble key facilities.

South Korea said it believed North Korea has started reassembly of its main Yonbgyon nuclear reactor, which was earlier being disabled and dismantled under a six-nation agreement for North Korea to end its nuclear weapons programme.

North Korea announced on August 14 that it had stopped disabling the nuclear plant where it produced weapons-grade plutonium, complaining about the US failure to remove it from a list of state sponsors of terrorism.

Last October, North Korea promised to disable its Yongbyon nuclear reactor in a six-party agreement with the United States, China, South Korea, Japan and Russia.

It demolished a cooling tower located next to the reactor in June, but has dragged its feet on agreeing to a verification regime for its nuclear disablement, a US precondition for scrapping sanctions. (dpa)