BEIJING (AFP) - US envoy Christopher Hill held talks Saturday with his Chinese counterpart amid stepped-up efforts to salvage a crumbling North Korean nuclear disarmament deal, a US embassy spokesman said. Hill briefed Chinese officials, including top nuclear negotiator Wu Dawei, as well as Sergey Razov, Russia's ambassador to China, on his visit to Pyongyang, the spokesman added. On Saturday evening he headed to Washington via Tokyo, the spokesman said. The US diplomat Friday described as "very substantive" the talks during his visit to Pyongyang, but gave no further details, saying he must first brief other parties to the six-nation agreement. A dispute over inspections of the North's nuclear facilities threatens to wreck last year's agreement under which the North shut down its nuclear programme in return for fuel aid and its removal from a US terrorism blacklist. The hardline North now threatens an imminent restart of its plutonium reprocessing plant at Yongbyon, an issue, which Hill called a "great concern." Hill left Pyongyang Friday for Seoul, where he briefed his South Korean and Japanese counterparts before heading to China, which chairs the six-nation talks that forged the deal. In an indication of the challenges facing Hill and the other envoys, the North was still moving to restart the plant despite the envoy's Pyongyang visit, the State Department said Friday. The North, which tested an atomic weapon in October 2006, began disabling its ageing reactor and other plants at Yongbyon in November 2007 under the pact with South Korea, Japan, Russia, the United States and China. But it announced last month it had halted work in protest at Washington's refusal to drop it from the US blacklist of countries supporting terrorism, as promised under the deal. Washington says the North must first accept strict outside verification of the nuclear inventory that Pyongyang handed over in June " a key topic in Hill's discussions in Pyongyang. US officials had said earlier Hill could offer the North a face-saving compromise in hopes of settling the verification dispute. Under the plan, North Korea may first give China a plan that includes sampling of nuclear material, access to key atomic sites and other verification provisions sought by the United States. President George W. Bush would then provisionally remove the North from the terrorism list, after which China would announce North Korea's acceptance of the verification plan. This would allow Pyongyang to assert that the delisting occurred before the verification plan was in place. North Korea, meanwhile, came under pressure at a meeting of the UN atomic watchdog in Vienna on Friday to resume the nuclear disablement process. In a draft resolution to the International Atomic Energy Agency's general conference, eight member countries said it was "important" that Pyongyang resume disablement work.