China and the United States have agreed to hold more trade talks in Beijing, Vice Premier Liu He said as U.S. President Donald Trump ordered his trade chief to begin the process of imposing tariffs on all remaining imports from China.

Liu voiced a measured optimism on reaching a deal, but said there were "issues of principle" on which China would not back down.

"Negotiations have not broken down," Liu, China's chief negotiator in the talks, said in Washington on Friday, according to state television on Saturday. "Quite the opposite, I think small setbacks are normal and inevitable during the negotiations of both countries. Looking forward, we are still cautiously optimistic."