WASHINGTON, June 25 (Reuters) -

The United States on Thursday blacklisted four steel, aluminum and iron companies operating in Iran's metals sector, as well as sales agents of Iran's largest steel manufacturer it said generate tens of millions of dollars for Tehran's metals industry.

The Treasury Department said in a statement it imposed sanctions on Tara Steel Trading GmbH, a Germany-based subsidiary of Mobarakeh Steel Co, three United Arab Emirates-based sales agents majority owned by the steel company, and Iran-based Metil Steel.

The Treasury said the sales agents "generated tens of millions of dollars annually from the foreign sale of Mobarakeh Steel Company products, providing significant contributions to the billions of dollars generated overall by Iran's steel, aluminum, copper, and iron sectors."

Mobarakeh Steel Co is the largest flat steel producer in the Middle East and North Africa and accounts for 1% of Iran's gross domestic product, the Treasury said. It has been designated by the United States under different authorities, including counterterrorism and for operating in Iran's metal sector.

Thursday's action also blacklisted three large aluminum, steel and iron producers in Iran, accusing them of contributing billions of dollars in sales and export of Iranian metals.

The sanctions freeze any U.S. assets held by the companies and generally prohibit Americans from dealing with them.

Thursday's actions did not appear related to a Reuters report published on Wednesday disclosing Iran's production of aluminum powder for use in missiles.

"The Iranian regime continues to use profits from metals manufacturers and foreign sales agents to fund destabilizing behavior around the world," Treasury Secretary Steven Mnuchin said in the statement.

Tensions between Washington and Tehran have spiked since Trump unilaterally withdrew in 2018 from the Iran nuclear deal struck by his predecessor, Barack Obama, and began reimposing sanctions that had been eased under the accord.