Europe tried to cajole Donald Trump to keep the U.S. in the Iran nuclear deal. That failed. Now the Old World is baring its teeth to save the accord.

French Foreign Minister Jean-Yves Le Drian Thursday slammed the U.S.’s push to reimpose sanctions on companies trading with Iran, saying it was “unacceptable” that European businesses should pay the price for Washington reneging on an agreement.

“We feel that the extraterritoriality of their sanction measures are unacceptable,” he said. “Europeans should not have to pay for the withdrawal from an agreement by the United States, to which they had themselves contributed.”

Le Drian said that Europeans would “do everything” to protect their interests and vowed to lead “tight negotiations” with the U.S. through the European Union.

The comments from France’s top diplomat, made in an interview with French daily Le Parisien, were the strongest condemnation yet from Europe against the U.S. withdrawal, which has left the landmark 2015 deal hanging by a thread and created a deep divide between Washington and many of its allies.

Calling the U.S. exit “a bad decision,” Le Drian said it undermined America’s word, indirectly incited nuclear proliferation and amounted to “an incitement to go to war on all sides.” He said the impacts of Tuesday’s decision were already registering, in the form of growing political uncertainty in the region and rising oil costs.

The other signatories — France, Britain, Germany, Russia, China, and Iran — have all vowed to work to uphold the deal in the wake of Trump’s egress. The biggest obstacle will be the reintroduction of U.S. sanctions on companies trading with Iran; if Iran loses the economic benefits of trade with the outside world, it will have no incentive to continue adhering to the accord.

Analysts say Europe’s best hope of preserving the deal will be pushing back against Washington to secure guarantees that certain areas of trade and investment with Iran can be protected from the threat of U.S. sanctions — and retaliate by imposing costs on American firms doing business in Europe if necessary.

But Washington has taken a hardline stance so far, warning European firms doing business in Iran that they have six months to wind up their investments or face sanctions.

A number of leading French firms, including Airbus, Peugeot and Renault, have signed billion dollar agreements with Iran since the nuclear deal was inked in 2015.

Le Drian will meet with his British, German and Iranian counterparts, and the European Union’s foreign policy chief Federica Mogherini in Brussels Tuesday to discuss how to keep the deal alive.