China on Saturday called Donald Trump "irresponsible" after the US president cancelled his top diplomat's trip to North Korea and suggested Beijing was stalling efforts to disarm Pyongyang.
US Secretary of State Mike Pompeo was due to make his fourth visit to the reclusive state next week for what he described as the next step towards the "final, fully verified denuclearisation of North Korea".
But Trump -- facing a slew of domestic problems and independent reports that North Korea has done little or nothing to roll back its nuclear programme -- vetoed the plan.
The US leader said Friday he had asked Pompeo not to go to Pyongyang "because I feel we are not making sufficient progress with respect to the denuclearisation of the Korean Peninsula".
Trump also stepped up his rhetoric against China, which has grown harsher as November congressional elections approach and as a trade war rages between the world's top two economies.
"Because of our much tougher trading stance with China, I do not believe they are helping with the process of denuclearisation as they once were" despite UN sanctions against Pyongyang, he added.
Beijing hit back at Trump's "capricious" accusations and said it had lodged an official diplomatic complaint over the comments.
"The US statement is contrary to basic facts and is irresponsible. We are seriously concerned about this," foreign ministry spokesman Lu Kang said in a statement posted on the ministry website.
"All parties concerned should... show more sincerity and flexibility, instead of being capricious and putting the blame on others."
China and the US are engaged in an escalating trade war, exchanging tit-for-tat tariffs on $100 billion worth of goods, with the most recent levies imposed by both sides on Thursday.
Stalling progress
Trump and the North's leader Kim Jong Un made a vague commitment to the "denuclearisation of the Korean Peninsula" at landmark talks in Singapore this year.
The US leader, who relishes unpredictability in negotiating, had at one point cancelled that meeting, citing North Korea's "open hostility".
But he soon backtracked and the summit went ahead on June 12.
Trump has touted his talks with Kim as a historic breakthrough, but both sides have since complained of stalling progress.
Washington has called for the economic embargo on North Korea to be maintained, saying the sanctions must remain in place until Pyongyang dismantles its atomic arsenal, and could even be tightened.
But China and Russia have argued that North Korea should be rewarded with the prospect of eased sanctions for opening up dialogue with the US and halting missile tests.
A UN agency recently reported it had not seen any indication that nuclear activities in North Korea have stopped.
"The continuation and further development of the DPRK's nuclear program and related statements by the DPRK are a cause for grave concern," said a report by the International Atomic Energy Agency (IAEA), using the initials of North Korea's official name.
North Korea is believed to be close to developing a miniaturized nuclear device and the ballistic missile capabilities to carry it anywhere in the continental United States.
Trump said on Friday that Pompeo would still head to North Korea "in the near future," saying this would likely occur when the US-China trading relationship is "resolved."
Earlier this week, Pompeo named a Ford Motor Co. executive as special envoy for North Korea to try to get disarmament back on track.
Stephen Biegun, 55, who is retiring as Ford's vice president for international governmental affairs, had been considered for the post of Trump's national security advisor before it went to John Bolton.
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