The actions freeze any assets the companies may have in U.S. jurisdictions and bar Americans from doing business with them.
The Treasury says one of the companies—SAD Import Export Co., of Tehran—also shipped weapons to the Syrian military on behalf of Iran's Defense Industries Organization. The Treasury says the shipments were meant to assist Syria's production of mortars and missiles for use against the Syrian civilian population.
The other blacklisted companies are Marine Industries Organization—plus director Mustafa Esbati—as well as Doostan International Co., and the Chemical Industries and Development of Materials Group.
Tehran insists its nuclear program is purely peaceful.