Iranian Foreign Minister Mohammad Javad Zarif paid an unannounced visit Sunday to the G-7 summit and headed straight to the buildings where leaders of the world's major democracies have been debating how to handle the country's nuclear ambitions. France's surprise invitation was a high-stakes gamble for French President Emmanuel Macron, who is the host of the Group of Seven gathering in Biarritz.

Zarif's plane left Tehran on Sunday morning and touched down a few hours later at the Biarritz airport, which has been closed since Friday to all flights unrelated to the official G-7 delegations.

Zarif, who is under U.S. sanctions, had been scheduled to go to Asia as part of a tour to seek support for Iran amid the American campaign against it since Mr. Trump withdrew the U.S. from Tehran's 2015 nuclear deal.

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U.S. Treasury Secretary Steve Mnuchin said Mr. Trump had not "set preconditions" on negotiations with Iran.

Zarif arrived as fissures emerged among G-7 leaders over how to deal with Iran.

Iranian Foreign Minister Mohammad Javad Zarif poses for a photograph during an interview with Agence France-Presse (AFP) at the residence of Iranian Ambassador in Paris on August 23, 2019. Getty

Macron said the leaders agreed during a dinner the night before that the French president could serve as a G-7 messenger to Iran. Mr. Trump denied agreeing to anything, and Macron was forced to play down his role and acknowledge Mr. Trump's status as "the president of the world's number one power."

The French official also said that based on Saturday night's dinner, France considers it important to check in with Zarif to continue to bring positions closer together and ease tensions. The official said the French are not "mediators" but think they can contribute to de-escalation.

Macron said he has no formal mandate to speak for the G-7 leaders in delivering a message to Iran, but that he would be able to address the issue in the context of what they agreed to during a dinner.

For several months, Macron has taken a lead role in trying to save the 2015 nuclear accord, which has been unraveling since Mr. Trump pulled the U.S. out of the agreement. His office said the G-7 leaders agreed he should serve as a go-between with Iran.

The G-7 leaders regrouped Sunday to focus on what they can do to boost growth at a time of heightened uncertainty. Manufacturers around the world are smarting from the trade dispute between the U.S. and China, which has led to new import taxes on hundreds of billions of dollars-worth of goods. Businesses don't know where tariffs will be imposed next.

The White House had said putting the economy on the agenda was Mr. Trump's idea, but the G-7 has for over four decades always included a focus on the economy. It was founded as a response to the Arab oil embargo in the 1970s and the recession that followed.