Any international firms that sell gasoline to Iran could face retribution under the U.S. sanctions including a possible ban from the U.S. financial system or denial of U.S. contracts. Cumhuriyet, an anti-government newspaper, said Tupras, Turkey's sole refiner and gasoline exporter, was vulnerable to the sanctions. It said state petroleum firm TPAO was readying to sign important agreements with Iran, and that the United States could sever all commercial ties with these companies. Tupras did not answer calls for comment. (Editing by Jon Hemming)