(Bloomberg) -- The US accused several Chinese companies of shipping machines that make counterfeit pills to the US and Mexico, and hit more than a dozen entities with sanctions as it looks to crack down on a trade officials say is contributing to the opioid crisis.

The sanctions were directed at companies and individuals that produce, sell and transport so-called pill presses, which are used to make illegal drugs look like legitimate pharmaceuticals, the US Treasury Department said in a statement. Officials said the counterfeit pills are often laced with fentanyl, a synthetic opioid, and frequently sent to the US.

As part of the scheme, the US says a Chinese company sold the machines to a pill supplier in Mexico that used them to create a series of “superlabs” capable of producing millions of fentanyl-laced pills every week. In one instance, the company sent the equipment through the US en route to Mexico.

Chinese Foreign Ministry Spokeswoman Mao Ning told reporters during a regular briefing on Wednesday that the responsibility for preventing machines from being used for drug making lies with the importer, adding that China will safeguard the rights and interests of Chinese companies and individuals.

Read more: US Targets Online Fentanyl Network Funded Through Cryptocurrency

The sanctions targeted seven companies and six people based in China, as well as one company and three people based in Mexico. One of the Chinese companies, Yason General Machinery Co., Ltd., has “worked with a Mexico-based pill equipment supplier and contact who previously provided equipment to a Sinaloa Cartel-linked individual,” the Treasury Department said.

One of the Chinese companies shipped die molds to the US that were used to create fake Xanax pills, Treasury said.

Treasury Under Secretary Brian Nelson, who leads the department’s office of Terrorism and Financial Intelligence, said the measures were a response to the “surge in fentanyl poisonings and deaths across the country.”

“Counterfeit pills laced with fentanyl constitute a leading cause of these deaths, devastating thousands of American families each year,” he said in a statement. “We remain committed to using all authorities against enablers of illicit drug production to disrupt this deadly global production and counter the threat posed by these drugs.”

--With assistance from Lucille Liu.

(Updates with comments from China’s foreign ministry in fourth paragraph. A previous version of this story corrected the number of people sanctioned in China in the fourth paragraph.)

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