BEIJING (AP) — China says it's not the source of the fentanyl that's killing Americans, contrary to President Donald Trump's recent tweets blaming China for the drug deaths.

Liu Yuejin, vice commissioner of China's National Narcotics Control Commission, said at a briefing Tuesday that Trump's claims are "completely groundless and untrue."

Trump blasted China last month in a Twitter thread in which he vowed to order all postal carriers to "SEARCH FOR & REFUSE all deliveries of fentanyl from China."

China has countered that it is making extensive efforts toward controlling the lethal opioid and should not be labeled the main source of fentanyl to the U.S.

In a sweeping change in May, China began regulating all fentanyl-related drugs as a class of controlled substances with the aim of curbing illegal drug trafficking.