The Treasury Department on Tuesday added a network of Russian and Iranian companies to its blacklist for shipping oil to Syria in violation of sanctions.

The network helps fuel the Syrian war effort of President Bashar Assad while providing revenue for Iran’s Islamic Revolutionary Guard Corps and the militant groups Hamas and Hezbollah, Treasury Secretary Steven Mnuchin said in announcing the sanctions.

“The Unites States in its continued efforts will not allow these dirty dealings to flourish,” Secretary of State Mike Pompeo told reporters on Tuesday. “Iran will not be allowed to exploit the international financial system to hide revenue streams it uses to fund terrorist activity.”

Placement on the list prohibits American entities or citizens from dealing with the companies and blocks any of the companies’ U.S. assets.

Mnuchin said the nine firms and people being added to the list are “critical actors” in a scheme to support Assad.

Those added to the list include Syrian national Mohammad Amer Alchwiki and his Russia-based company, Global Vision Group. Also sanctioned was Promsyrioimport, a subsidiary of Russia’s Energy Ministry, which helps facilitate payments to Iran, according to the Treasury statement. The deputy head of Promsyrioimport, Andrey Dogaev, was also sanctioned. Other designated entities include Iran-based Tadbir Kish Medical and Pharmaceutical Company and the Moscow-based Mir Business Bank.

In Moscow, officials dismissed the sanctions as illegal.

“The fresh American sanctions are absolutely illegal and unlawful,” Leonid Slutsky, head of the foreign affairs committee in the lower house of the Russian parliament, was quoted as saying by the Interfax news agency. “The United States is the only country in the world that uses extraterritorial law and violates other countries’ jurisdiction through legislation.”

There was no immediate reaction from Tehran.

(AP)