"We are here today to deliver a message on behalf of the United States government. We know who is responsible for poisoning the American people with fentanyl," U.S. Attorney General Merrick Garland told reporters.

"We know that this global fentanyl supply chain, which ends with the deaths of Americans, often starts with chemical companies in China."

The U.S. Treasury Department in a statement said it imposed sanctions on 28 people and entities involved with the international proliferation of illicit drugs, including a large China-based network.

The move marks the latest Chinese targets Washington has hit with sanctions related to fentanyl, as the administration seeks to stem imports of the drug.

The Justice Department also unsealed eight indictments charging eight China-based companies and 12 of their employees with crimes relating to fentanyl and methamphetamine production, distribution of synthetic opioids, and sales resulting from precursor chemicals.

None of the defendants has been arrested so far and the Chinese government did not work with U.S. authorities on the investigations, Garland said.

Liu Pengyu, spokesperson for China's embassy in Washington, said China strongly condemned Tuesday's move, adding that the Chinese government takes a firm stance on counter-narcotics.

"The U.S., however, in disregard of China’s goodwill, has been scapegoating China through the tactics of sanctioning, smear and slander. This has seriously eroded the foundation of China-U.S. cooperation on counter-narcotics," Liu said.

U.S. Secretary of State Antony Blinken, during his visit to China in June, said he made clear Washington needs much greater cooperation from China on stemming the flow of fentanyl and that the sides had agreed to explore setting up a working group on the matter.

Tuesday's announcement came the day before Garland was due to travel to Mexico with other senior U.S. officials. Fentanyl trafficking is expected to be a major subject of discussion.

U.S. prosecutors accused some of the chemical manufacturing companies of shipping chemicals used to make fentanyl to the U.S. using fake shipping labels and other mechanisms to avoid detection. Other shipments went to Mexico's powerful Sinaloa drug cartel, prosecutors said.

The Treasury accused the China-based network of being responsible for the manufacturing and distribution of fentanyl, methamphetamine and MDMA precursors.

It said the network is capable of synthesizing multi-thousand-kilogram quantities of fentanyl, methamphetamine, and MDMA precursors and other illicit chemicals.

So-called fentanyl precursors are chemicals used to produce the powerful synthetic opioid that has fueled a rise in drug overdose deaths in the United States in recent years.

Also hit with sanctions were two entities and one person based in Canada.

Tuesday's sanctions action freezes any U.S. assets of those targeted and generally bars Americans from dealing with them.