WASHINGTON (Reuters) - U.S. President Donald Trump on Thursday accused his Chinese counterpart of failing to meet promises to stem a deluge of the synthetic opioid fentanyl into the United States, after months of praising Chinese President Xi Jinping for his pledges.

U.S. President Donald Trump departs for travel to Cincinnati, Ohio from the South Lawn of the White House in Washington, U.S., August 1, 2019. REUTERS/Carlos Barria

“My friend President Xi said that he would stop the sale of fentanyl to the United States - this never happened and many Americans continue to die,” Trump said in a tweet.

“We’re losing thousands of people to fentanyl,” he later told reporters.

The Chinese embassy did not immediately respond to a request for comment.

Fentanyl is an opioid painkiller 50 times more potent than heroin, and has a central role in the devastating U.S. opioid crisis. In the United States, fentanyl and all of its analogues are controlled substances subject to strict regulation.

More than 28,000 synthetic opioid-related overdose deaths, mostly from fentanyl related substances, were recorded in 2017, according to the U.S. Centers for Disease Control and Prevention.

Trump’s complaints came as he also announced a new round of tariffs on Chinese imports starting Sept. 1, after negotiators failed to make progress in U.S.-China trade talks.

Trump has made battling the opioid epidemic a priority since taking office and he pressed Xi to halt the flow of fentanyl and related substances from China, which U.S. officials say is the main source of the powerful synthetic opioids.

Xi promised Trump at a summit in Argentina last December that he would act.

China later announced that it expanded on May 1 the list of narcotics subject to state control to include the more than 1,400 known fentanyl analogues, which have slightly different chemical makeups but are all addictive and potentially deadly, as well as any new ones developed in the future.

The policy change was supposed to shut down the illicit production and online sales of the drugs, which are mainly delivered to the United States by mail.

The White House Office of National Drug Control Policy said after Trump’s comments on Thursday that the administration had not “directly seen any large-scale seizures or law enforcement action by the Chinese on fentanyl.”

“Too many Americans do continue to die from these deadly drugs, most of which come from China,” it said in a statement. “We’ll continue to press China to follow through on the promise they made to keep fentanyl out of our communities.”

U.S. officials and experts had been skeptical that Beijing would take meaningful action, with some saying any crackdown would depend on progress in resolving the U.S.-China trade war.

Derek Scissors, a resident scholar at the American Enterprise Institute think tank, said that skepticism was well placed.

“What the Chinese have effectively said is we should forget what they said just a few months ago. If they don’t like the trade situation, the fentanyl and related products will continue to flow,” he said in an email on Thursday.

“The Chinese government accuses us, with some reason, of not keeping strictly to our word,” he said. “When we back away from our word, the way they have here, does anyone die?”