"I can’t think for an instant that all the Iranian authorities have decided on total isolation of their country. I think that, to the contrary, it would be in their interest to turn towards negotiation," Foreign Minister Philippe Douste-Blazy told France Inter radio.
He noted that the UN Security Council had acted "in a united manner" to pass its resolution Saturday against Iran, imposing sanctions on its nuclear industry and ballistic missile programmes.
Iran responded Sunday by saying it would install 3,000 uranium enriching centrifuges at a key nuclear plant to reinforce its controversial nuclear programme.
Iranian President Mahmoud Ahmadinejad dismissed the UN resolution as just a "scrap of paper" and declared Iran "is a nuclear country".
Douste-Blazy told the French radio station: "Unanimity and firmness will lead to the isolation of this country, even if Iran doesn’t understand that."
He warned Iran not to enter into that "spiral", and, later on a visit to the southwest city of Toulouse in France, he called on Tehran to "return to reason".
He added: "The ball is now on Iran’s court — either it accepts negotiations, as France wants, or else it will isolate itself."