The United States has seen important action by China on curbing fentanyl, a senior official said Friday after talks in Beijing, but he acknowledged the risk that friction between the two powers would "blow up" progress.

Making good on a commitment during a November summit between Presidents Joe Biden and Xi Jinping, a US delegation held an inaugural meeting this week in China on the flow of fentanyl, the powerful painkiller behind an addiction epidemic in the United States.

"We recognized some initial steps by the PRC," said Todd Robinson, the assistant secretary of state dealing with narcotics and law enforcement, referring to the People's Republic of China.

"Is it significant? Absolutely," he told reporters on his return to Washington, while adding the action was not yet enough.

US officials have long charged that China is complicit in the trade of fentanyl, which is many times more powerful than heroin and is responsible for more than 70,000 overdose deaths a year in the United States.

China banned fentanyl exports in 2019 but US officials say that it is still the primary source of precursor chemicals to the synthetic opioid, which are then put together by cartels in Mexico and then smuggled into the United States.

Since Xi's promise to Biden at the summit in California that China would act, "it is clear they have gone to certain companies and either warned them or shut them down," Robinson said.

He described Chinese government efforts as effective, saying that after the 2019 ban on fentanyl exports, "it stopped almost immediately."

Robinson described the mood at the talks as "very positive," with the Chinese hosts speaking to the delegation at length including over a banquet.

But he said that a resurgence of US-China tensions was "absolutely on the radar" of the United States.

"It wouldn't be the first time if, you know, another balloon flies over the United States or X congressman decides to visit Taipei," he said, referring to a row last year over an alleged Chinese surveillance balloon and Beijing's objections to US support for Taiwan.

The United States will see "how much we can get done in the fastest amount of time, and always cognizant that something could blow it all up."