The U.S. Justice Department Friday filed criminal charges against four Chinese chemical manufacturing companies and eight individuals over allegations they illegally trafficked the chemicals used to make fentanyl — a highly addictive painkiller that has fueled the opioid crisis in the United States.

The indictments mark the first time the United States has sought to prosecute any of the Chinese companies responsible for manufacturing the precursor chemicals used to make the painkiller.

The companies at the heart of the three separate indictments are accused of selling precursor chemicals to the Sinaloa Cartel in Mexico, who in turn have helped to flood the United States with the drug.

The case comes about two months after the Justice Department previously charged leaders of the cartel with running a fentanyl trafficking operation fueled by Chinese chemical companies, including three sons of Joaquin "El Chapo" Guzman, the onetime leader of the Sinaloa Cartel now imprisoned in the United States.

Deputy Attorney General Lisa Monaco, the department's No. 2 official, said on Friday the cases "break new ground by attacking the fentanyl supply chain at its origin."

"Fentanyl poses a singular threat, not only because the smallest doses can be lethal, but because fentanyl does not occur in nature. It is entirely man-made," she added.

The Chinese Embassy did not immediately respond to a request for comment on the allegations.

In Manhattan's Southern District, federal prosecutors announced the unsealing of an indictment against the China-based chemical company Hubei Amarvel Biotech, along with its executives Qingzhou Wang, 35, Yiyi Chen, 31, and Fnu Lnu, also known as Er Yang, with fentanyl trafficking, precursor chemical importation, and money laundering offenses.

Wang and Chen were arrested by the federal agents from the U.S. Drug Enforcement Administration on June 8 and ordered detained by a federal magistrate judge in Honolulu, Hawaii on June 9 until they can be transported to New York City to appear before the judge handling the case.

Yang remains at large.

In the Eastern District of New York, meanwhile, prosecutors announced the unsealing of two more indictments against three other Chinese companies and individuals, accusing them of conspiring to manufacture and distribute fentanyl in the United States.