China on Tuesday denied it was to blame for fentanyl deaths in the United States after President Donald Trump accused Beijing of reneging on its promise to crack down on the opioid.
US authorities have long accused China of being the main source of the potent drug, which caused 32,000 overdose deaths in the United States last year alone.
In an apparent gesture to Washington amid the US-China trade war, Beijing announced a crackdown on fentanyl earlier this year, designating all analogues of the drug as controlled substances from May 1.
The move aimed to prevent smugglers from skirting the law by changing formulas to make drugs similar to the painkiller.
Fentanyl sellers have used parcel services to send the drug to the United States, and China had also vowed to step up customs checks.
But Trump wrote on Twitter last month that while Xi had pledged to stop exports of fentanyl, "this never happened, and many Americans continue to die!"
Liu Yuejin, vice commissioner of China's National Narcotics Control Commission, countered on Tuesday that no case of fentanyl smuggling has been reported since the May 1 ban.
"What President Trump concluded on Twitter is groundless," Liu said.
"China has strengthened its control of fentanyl but the number of deaths linked to this substance continue to rise in the United States," Liu said, suggesting that the drug came from elsewhere.