President Trump ordered U.S. shipping companies to block shipments of the opioid painkiller fentanyl into the country from China.

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"I am ordering all carriers, including Fed Ex, Amazon, UPS and the Post Office, to SEARCH FOR & REFUSE all deliveries of Fentanyl from China (or anywhere else!)," Trump tweeted Friday.

"Fentanyl kills 100,000 Americans a year. President Xi said this would stop - it didn’t," he continued. "Our Economy, because of our gains in the last 2 1/2 years, is MUCH larger than that of China. We will keep it that way!"

The comments come as China announced a new round of retaliatory tariffs on about $75 billion worth of U.S. goods. Trump said on Twitter that he would respond to the tariffs Friday afternoon.

Trump's director of trade and manufacturing policy, Peter Navarro, echoed the president's message in an interview with FOX Business anchor Maria Bartiromo Friday morning.

"He has absolutely galvanized the American people and Capitol Hill behind his China policy, and we know why," Navarro said of Trump. "China steals our stuff, they flood our communities with fentanyl and everything in between."

China added fentanyl products to the country's list of narcotics subject to state control after President Xi Jinping met with Trump in December 2018, but the White House says it has not seen substantial action on blocking major shipments.

UPS responded to the tweets, telling FOX Business it "follows all applicable laws and administrative orders of the governments in the countries where we do business."

"We work closely with regulatory authorities to monitor for prohibited substances," UPS said in a statement.

FedEx said it "already has extensive security measures in place to prevent the use of our networks for illegal purposes."

"We follow the laws and regulations everywhere we do business and have a long history of close cooperation with authorities," the company told FOX Business. "FedEx supported passage of the STOP Act and encourages accelerated implementation and enforcement of its provisions to protect the health and safety of the American people.”

Suzanne O'Halloran contributed to this report.