Washington CNN  — 

The Justice Department is taking its war on drugs worldwide.

Deputy Attorney General Rod Rosenstein announced the first-of-its-kind indictment against two Chinese nationals who were allegedly manufacturing and trafficking to the US fentanyl and fentanyl analogues, substances that can be 50 times as potent as heroin.

According to the Centers for Disease Control, an estimated 20,000 Americans were killed by fentanyl and fentanyl analogues in 2016.

The Chinese nationals were using the Internet and dark web to sell fentanyl to US customers, many of whom were too inexperienced or unaware to realize they were buying the highly pure substance, Rosenstein told reporters Tuesday.

“They use multiple identities to disguise their activities and their shipments and to obscure the trail of profits going back to China,” Rosenstein said. “They take advantage of the fact that the fentanyl molecule can be altered in numerous ways to create a fentanyl analogue that is not listed as illegal under US or Chinese law. When regulators are able to identify the new fentanyl and make it illegal, the distributors quickly switch to a new, unlisted fentanyl analogue.”

Investigators tracked down the two Chinese defendants, Xiaobing Yan, 40, and Jian Zhang, 38, and the chemical plants they operated in China after a series of local law enforcement crackdowns in Mississippi and North Dakota, according to the indictment.

A routine traffic stop in Mississippi in 2013 first unearthed a domestic drug ring tied to Yan. The ring sold synthetic cathinones and cannabinoids, commonly known as “spice” or “bath salts,” and delivered the products through parcel delivery services, according to the Justice Department. Yan allegedly operated websites advertising the deadly fentanyl and sold it directly to customers in several cities around the country, Rosenstein said.

Zhang was pinpointed in the wake of the death of an 18-year-old who died after a fentanyl overdose in Grand Forks, North Dakota. Federal agents identified another Grand Forks resident as the source of the fentanyl, and discovered that the buyer had used crypto-currency Bitcoin to buy the drugs over the Internet for more than a year, “using an encrypted website on the Dark Web,” Rosenstein said. Prosecutors were eventually able to trace the drugs to Zhang’s distribution network in China.

Five Canadian citizens, two residents of Florida, and one resident of New Jersey were also indicted in connection with Zhang’s drug ring on charges of conspiracy to distribute the drugs in at least 11 states, according to the Justice Department.

The indictments were announced after President Donald Trump’s nominee for drug czar, Rep. Tom Marino of Pennsylvania, withdrew his name from consideration for the position. The withdrawal came amid fallout from a joint investigation by The Washington Post and CBS’ “60 Minutes” that revealed Marino took nearly $100,000 from the pharmaceutical lobby while sponsoring legislation that made it easier for drug companies to distribute opioids, but also thwarted the Drug Enforcement Agency’s efforts.

Rosenstein said DOJ will review the law, but didn’t say whether it should be repealed.

“I’m very concerned about it,” he said. “I’ve talked to the attorney general about it. We’re going to review it.”