Iranian Foreign Minister Javad Zarif arrived unannounced at the G7 summit on Sunday in an intervention aimed at easing Tehran's nuclear deal crisis.
But the unexpected arrival risked angering US President Donald Trump, who was not told of the Iranian's invitation.
Mr Zarif arrived at the invitation of G7 summit host France, which has taken the lead in trying to ease tension between Tehran and the US, at a time when America has increased sanctions against the regime and tried to seize one of its oil tankers.
His arrival took the US delegation by surprise and appears not to have been discussed during an unscheduled two-hour meeting on Saturday between French President Emmanuel Macron and Mr Trump.
A White House official said Mr Trump was not warned by France. Asked about the arrival of Mr Zarif, who is on a US sanctions list, Mr Trump said: “No comment.”
But a senior French official told AP that Mr Macron personally told the US president about his invitation.
French and Iranian officials played down the prospects of a face-to-face meeting with Mr Trump, who last year pulled the US out of the nuclear deal and tightened sanctions against Iran.
"No meeting with Americans in Biarritz," Iranian UN mission spokesman Alireza Miryousefi posted on Twitter.
Mr Zarif’s first appointment was with French Foreign Minister Jean-Yves Le Drian at the summit in the French coastal resort of Biarritz.
Mr Trump’s policy of exerting maximum pressure on Iran has alienated European leaders.
They have sought to continue trading with Tehran but banks and businesses have proved wary because of fears that they would be locked out of the US financial system.
The meeting followed confusion at the summit after leaders of the world’s leading democracies gave mixed messages about their plans for dealing with Iran.
After Mr Zarif left the summit, it was unclear whether progress had been made to ease tensions between Iran and the West.
The forum has been marked by disputes over trade, climate change and whether Russia should be readmitted to the G7.
A French official claimed the G7 had agreed on Saturday night to allow Mr Macron to talk to Tehran and try to tackle the growing crisis in the Arabian Gulf.
But Mr Trump, who has taken the hardest diplomatic line against Iran, immediately distanced himself from any suggestion that the leaders of the US, Britain, Germany, Italy, Canada, Japan, France and the EU have reached agreement on a joint message.
"No, I haven't discussed that," Mr Trump said on Sunday, shortly after Mr Macron claimed that a message had been agreed to with the other leaders.
Mr Macron met Mr Zarif on Friday to discuss plans to ease the crisis, which included cutting some US sanctions or a way to compensate Iran for economic losses. In return Iran would have to comply fully with the nuclear deal.
The Iranian foreign minister also met diplomats from Germany and Britain at the Biarritz city hall.
“Road ahead is difficult. But worth trying,” Mr Zarif tweeted after holding more than three hours of talks.
“The discussions that were held between the president and Mr Zarif were positive and will continue,” a French official said after the meeting, declining to take detailed questions.
The G7 leaders discussed Iran at the opening summit dinner when the French side insisted that a deal had been agreed to.
“As president of the G7, the president did indeed get the power to discuss and send a message to Iranian authorities on the basis of the exchanges we had last night,” said a French official.
Discussions with Mr Zarif were even more complicated after he was last month put on a US sanctions list.
The US Secretary of State Mike Pompeo said the decision to designate Iran’s chief diplomat was because he was just as complicit in the regime’s "outlaw behaviour" as the rest of supreme leader Ayatollah Ali Khamenei's "mafia”.
The US and the EU have taken starkly different approaches towards Iran, highlighted by the seizure and later release of the Iranian tanker Grace 1 off the Gibraltar coast.
Washington has continued to seek to detain the ship, forcing it to divert from its planned course to Greece, where it was due to arrive on Sunday.
Mr Macron’s attempt at a breakthrough in the Iran impasse highlighted the intractability of many other issues on the agenda for the three-day meeting.
Mr Trump arrived on Saturday with Iran just one of many policy differences with his G7 partners.
Officials said the most contentious discussion over the opening leaders’ dinner was the debate about whether to allow Russia to rejoin the group after being thrown out over the invasion of Ukraine in 2014.
Mr Trump had threatened to impose sanctions on French wine in retaliation for French plans for a digital services tax, which would hit technology majors such as Apple and Google.
But he criticised the “fake and disgusting news” media for suggesting that relations between the leaders were tense.
The cracks appeared after Mr Trump's first meeting of the day, with new British premier Boris Johnson, his closest ally at the talks, when the two disagreed over the US trade war with China.
Mr Johnson said he was in favour of “trade peace”.
The discord was spelt out by Donald Tusk, the European Council president, who said before the meeting that it was “increasingly hard” to find common ground.
"This is another G7 summit that will be a difficult test of unity and solidarity of the free world and its leaders," Mr Tusk said. "This may be the last moment to restore our political community."
Mr Johnson, whose amicable meeting with Mr Trump was to be followed by a more difficult session with Mr Tusk over Brexit, also alluded to the tension.
During a long handshake on Sunday, Mr Johnson told Mr Macron: "You did very well last night. My God, that was a difficult one."
Mr Macron has put the environment at the centre of his agenda for the summit but faced disagreement over his desire to halt an EU trading deal with Brazil until it tackled fires in the Amazon.
He also faced protests on Sunday from demonstrators who claim that his challenges to global leaders to tackle climate change have not been matched by his actions.
