The discussions in Beijing, led by US Commerce Secretary Wilbur Ross and Chinese Vice Premier Liu He, were meant to ease tensions after Washington said on Tuesday it would follow through with tariffs on Chinese imports despite a truce reached between the two sides last month.
If the U.S. moves forward with sanctions, "all the economic and trade achievements negotiated by the two parties will be void", Xinhua state news agency said in a statement.
The talks focus on adding details to China's May 19 promise to narrow its politically volatile surplus in trade in goods with the United States, which reached a record US$375.2 billion previous year.
Beijing said the two sides had made "positive and concrete progress" on matters like increasing agricultural and energy imports but said details were left for "both sides to finalise".
The United States and China have threatened tit-for-tat tariffs on goods worth up to $150 billion each.
Beijing warned all the commitments it had made so far were premised on "not fighting a trade war".
Mnuchin, speaking at a G7 finance leaders meeting in Canada where he was the target of U.S. allies' anger over steel and aluminium tariffs, said the China talks would cover other issues, including the Trump administration's desire to eliminate Chinese joint venture requirements and other policies that effectively force technology transfers.
A short statement, carried by the official Xinhua news agency, made no mention of any specific new agreements after U.S. commerce secretary Wilbur Ross met Chinese vice premier Liu He.
China said Sunday that any trade deals now being discussed with the USA will not go into effect if the Trump administration implements proposed tariffs on Chinese goods, according to multiple media reports.
Last week the White House announced it would impose curbs on Chinese investment and purchases of US high-tech goods and on visas for Chinese students. China has also threatened to hit back with tit-for-tat tariffs on tens of billions of dollars in USA goods.
Liu offered the USA team a "special welcome" to Beijing for the talks.
Beijing has portrayed itself as a defender of free trade, despite China's status as the most closed major economy, in response to Trump's support for import controls.
Trump is pressing Beijing to narrow its politically volatile trade surplus with the United States, which reached a record $375.2 billion U.S. past year. China pledged to take steps to "substantially" reduce the USA trade deficit, including by buying more American farm goods and energy, though it didn't commit to a dollar amount.
Ross and the large American delegation had dinner Saturday evening with their Chinese hosts.
"The more Trump is irritating allies and asking Chinese to buy stuff, the better off they are, because he's not sitting there and attacking the hard issues", the person said. "This is about structural changes", Mnuchin told reporters in Whistler, Canada, at the close of a summit of G-7 finance chiefs.
"There are structural changes that allow our companies to compete fairly".