Reuters reported that the Indian refiner Reliance quit selling gasoline and diesel to Iran last year after French banks BNP Paribas and Calyon stopped offering credit on the deals, four company and industry sources said on Thursday.

BNP and Calyon, the investment bank arm of Credit Agricole, likely stopped offering Letters of Credit (LCs) — a standard form of payment guarantee in the oil trade — because of political pressure from Western nations that believe Tehran is trying to develop nuclear weapons, one of the sources said.

The move by the banks is a sign that the U.S.-led campaign to isolate Tehran over its nuclear programme is making it more difficult to do business with the Islamic Republic.

Swiss-based independent trader Vitol, Iran’s biggest supplier of gasoline, decided to end its long-running contract to provide fuel to the country this year after losing money on the deal, an industry source said last month. Many bank majors including Switzerland’s UBS AG and Germany’s Deutsche Bank AG have decided to cut some or all of their ties with Iran in the face of political pressure.