The U.S. on Thursday unveiled a new round of sanctions targeting people and companies linked to Iran and to what it said was an illicit banking network used to facilitate Tehran’s access to the global financial system.

The U.S. said it placed the penalties on 39 firms linked to a shadow banking system that helped to obfuscate financial activity between sanctioned Iranian firms and their foreign buyers, namely for petrochemicals produced in Iran.

The Treasury Department said the companies – from Hong Kong to the United Arab Emirates (UAE) – made up a "significant ‘shadow banking’ network" that gave cover to sanctioned Iranian entities to disguise petrochemical sales with foreign customers.

The latest U.S. move against Iran comes as efforts to revive the 2015 nuclear deal have stalled, while ties between Tehran and the West have become increasingly strained as Iranians keep up anti-government protests.

Washington has targeted Chinese companies for exporting Iran’s petrochemicals as the prospects of reviving the nuclear pact have dimmed.

"Iran cultivates complex sanctions evasion networks where foreign buyers, exchange houses, and dozens of front companies cooperatively help sanctioned Iranian companies to continue to trade," said Deputy Treasury Secretary Wally Adeyemo.

"Today’s action demonstrates the United States’ commitment to enforcing our sanctions and our ability to disrupt Iran’s foreign financial networks, which it uses to launder funds," Adeyemo noted.

Secretary of State Antony Blinken said in a written statement that the U.S. "will continue to disrupt attempts to evade U.S. sanctions."

Also included in the Thursday announcement was a set of financial penalties on a China-based network of firms and one person accused of being responsible for the sale and shipment of thousands of drone components to Iran.

Iran is accused of supplying Russia with drones to bomb Ukrainian civilians as the Kremlin continues its invasion of Ukraine.

Among other things, the sanctions deny the people and firms access to any property or financial assets held in the U.S. and prevent American companies and citizens from doing business with them.

A former Treasury Department official, Brian O’Toole, said Thursday’s action would dent Iran’s ability to keep moving oil and get paid.

"This is a pretty big deal because this kind of thing should impact what Iran can sell," O’Toole said.

The sanctions come one day after Iranian prison officials, and others were hit with sanctions over the treatment of young women and girls.

Tensions between the U.S. and Iran are high amid months of anti-government protests in Iran and Western anger at Iran’s export of attack drones to Russian forces fighting in Ukraine.