– In the wake of President Donald Trump’s decision to withdraw from the Iran nuclear deal, European leaders on Tuesday began discussions about how they might sweeten the deal to keep Iran from restarting its nuclear program and stand up to coming U.S. sanctions on companies that do business in Iran.

The top diplomats of Britain, France and Germany met in Brussels with Iranian Foreign Minister Mohammad Javad Zarif and the European Union’s chief diplomat, Federica Mogherini. Those countries were all signatories of the 2015 deal that aimed to prevent Iran from building a nuclear weapon in exchange for economic incentives.

Trump’s decision to pull out of the agreement unilaterally has created one of the biggest foreign policy crises of his presidency, infuriating Washington’s closest allies in Europe and driving them to consider whether to order European businesses doing business in Iran to ignore U.S. sanctions. That would be the diplomatic equivalent of a slap in the face.

In Tuesday’s meetings, Europe and Iran sought to preserve the landmark agreement. “The U.K. and our European partners continue to view the nuclear deal as vital for our shared security and remain fully committed to upholding it,” said British Foreign Secretary Boris Johnson.

Zarif said he was optimistic that Iran and the other parties to the agreement could find a way to keep it alive.

Trump’s decision has created a tricky game of strategy for other countries that remain committed to the agreement, which was endorsed by the U.N. Security Council after years of negotiations.

Iranian President Hassan Rouhani has staked his political legacy on delivering prosperity for Iranians through the deal, which is now threatened by the new U.S. sanctions. Iranian hard-liners who always felt the agreement made too many concessions may be emboldened to restart nuclear enrichment, but they could risk U.S. and Israeli airstrikes.

The split Iranian position was clear Tuesday, with other leaders adopting a tough stance in Tehran as Zarif offered a friendlier stance in Brussels.

“We have the capacity and we are ready to resume our nuclear activities to a much higher level if the talks fail with Europeans to save the nuclear deal after America’s exit,” Iranian Atomic Energy Organization head Ali Akbar Salehi was quoted as saying by Iran’s Fars news agency, Reuters reported.

The leaders of the 28 nations of the European Union plan to discuss their response to the U.S. pullout at a Wednesday summit in Bulgaria. One option is to invoke a never-before-used “blocking mechanism,” directing E.U. businesses to ignore U.S. sanctions.

But diplomats have doubts about whether E.U. countermeasures would be effective, since most big businesses are unlikely to risk their access to the U.S. market in favor of much smaller potential rewards in Iran.