The Department of Justice announced Friday that it had charged four chemical companies based in China and eight Chinese nationals for the trafficking of fentanyl precursor chemicals into the U.S. for the first time. 

The agency said the charges are over crimes related to fentanyl production, distribution and sales resulting from the precursor chemicals. 

The announcement included the arrest of two individuals and the unsealing of three indictments in the southern and eastern districts of New York. 

The indictments allege, specifically, that the defendants had knowingly manufactured, marketed, sold and supplied precursor chemicals for fentanyl production in the U.S., which is a violation of federal law.

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The Drug Enforcement Agency seized more than 200 kilograms of fentanyl-related precursor chemicals during these investigations. 

That is a quantity the Justice Department said could contain enough deadly doses to kill 25 million Americans.

In the southern district of New York, charges were brought against a China-based manufacturer and supplier of fentanyl precursor chemicals, its principal executive and two of its employees for their role in an international fentanyl trafficking conspiracy.

The department alleged they had openly advertised the sale of fentanyl precursors online, using deceptive packaging and guaranteeing "100% stealth shipping." Further, the indictment details meetings and communications between the defendants and an individual purporting to be a fentanyl trafficker in Mexico with operations in the U.S.

"What the defendants did not know at the time is that the purported traffickers they were dealing with were, in fact, DEA confidential sources. And the 200 kilograms of fentanyl-related precursors they shipped to the U.S. were received by DEA agents," U.S. Attorney General Merrick Garland said in a speech. 

In two separate indictments in the eastern district of New York, three other Chinese-based companies and five of their employees were charged with conspiracy to manufacture and distribute fentanyl.

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The companies also supplied precursor chemicals to the U.S. and Mexico, among other places, and all three openly advertised their products globally and guaranteed that those sent to the U.S. and Mexico would not be detected or intercepted. 

They mislabeled packages and also made declarations at border crossings, according to the department. 

Garland noted that they also added what are known as "masking" molecules to their fentanyl precursor chemicals. With that addition, the chemical signature of the precursor is changed, and – when it is shipped – it appears to be a new, non-fentanyl precursor substance.

The companies provided instructions about how to remove the masking molecules and return the chemical to its original form as a fentanyl precursor. 

"The actions we are announcing today should make clear that the U.S. Justice Department is accelerating our efforts to disrupt the manufacture and trafficking of fentanyl at every stage and in every part of the world," Garland stated.

He "strongly" urged the Chinese government to "take decisive action to address the role that China-based chemical and pharmaceutical companies play in fentanyl drug production and trafficking" and said that the U.S. is ready to "work together to address this global challenge."

The Department of Justice notes that fentanyl is a highly addictive synthetic opioid that is 50 times more potent than heroin and 100 times more potent than morphine. 

Fentanyl is now the leading cause of death for Americans ages 18 to 49. 

The department noted that an indictment is "merely an allegation" and that all defendants are presumed innocent until proven guilty beyond a reasonable doubt in a court of law.

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A spokesperson for the Chinese Embassy condemned the charges, according to The Associated Press, accusing the U.S. government of seeking to shift the blame for its domestic drug problem.

Liu Pengyu, a spokesperson for the embassy, charged U.S. prosecutors with imposing a "long-arm jurisdiction," saying that the move could harm counter-narcotics operations between the two countries.

"The incident was a well-planned entrapment operation by the U.S. side, which seriously infringed upon the legitimate rights of relevant enterprises and individuals," the spokesperson said. "China strongly condemns it."

The Associated Press contributed to this report.