WASHINGTON - The US Treasury took action Wednesday to crack down on Chinese traffickers of deadly fentanyl, sanctioning producer-exporters and warning banks on financial schemes used to distribute the synthetic opioid behind thousands of US overdose deaths.

The Treasury identified Zheng Fujing, 36, and a company he controls, Qinsheng Pharmaceutical Technology, and a partner, Zheng Guanghua, as a major, Shanghai-based production fentanyl production and trafficking organization.

The Zheng drug trafficking organization, the Treasury said, produced and shipped hundreds of controlled substances, including fentanyl analogues such as carfentanil, which is 100 times more potent than fentanyl.

"Zheng created and maintained numerous websites to advertise and sell illegal drugs in more than 35 languages," it said.

Moreover, it said, Zheng was producing counterfeit cancer pills that replace the active cancer-fighting ingredient with "dangerous synthetic drugs."

Yan, meanwhile, produces and trafficks in synthetic opioids, cannabinoids, and cathinones, and amphetamine-like drug, the Treasury charged.

"Yan has tried to evade prosecution by modifying the chemical structure of his synthetic analogues based on his monitoring of legislation and law enforcement activities in the United States and China," the Treasury said.

All three men have already been indicted in separate trafficking cases in the United States.

The Treasury's designation of the three as "significant foreign narcotics traffickers" under the US Kingpin Act allows the Treasury to use more sanctions and controls to attack their networks.

The Treasury said it had also issued an advisory to banks and other financial institutions describing how synthetic opioid producers and traffickers operate in financial networks, with the aim of closing off their ability to produce and sell their drugs.

"We are making the financial sector aware of tactics and typologies behind illicit schemes to launder the proceeds of these fatal drug sales, including transactions using digital currency and foreign bank accounts," said Kenneth Blanco, the head of the Treasury's Financial Crimes Enforcement Network.

The Treasury said both the Zheng and Yan groups used digital currencies like bitcoin for production operations and sales.