France has told its diplomats and foreign ministry officials to postpone indefinitely all non-essential travel to Iran, citing a foiled bomb plot and a hardening of Tehran’s attitude towards France.

Any hardening of relations with France could have wider implications for Iran. France has been one of the strongest advocates of salvaging a 2015 nuclear deal between Iran and world powers, which U.S. President Donald Trump pulled out of in May.

Iran’s economy has been hammered by the prospect of the re-imposition of U.S. sanctions that had been lifted under the deal. European countries including France have pledged to try to soften the economic blow, but have been unable so far to persuade their firms to defy Washington and stay in Iran.

French oil and gas major Total and its carmakers PSA and Renault have led an exodus of European companies from Iran, fearful of the extra-territorial reach of Washington’s sanctions.