Jean-Yves Le Drian will tell Iran it must address the West's misgivings about its ballistic missile programme and military activities around the Middle East - points the White House says need attention if the nuclear pact is to survive.
"We're not going to be Donald Trump's envoys or Iran's defence lawyers," said a French diplomatic source. "We have our own concerns and will talk to the different sensibilities of the Iranian system to get our point across."
Trump has said European allies must help "fix" the nuclear deal before a May 12 deadline.
Le Drian said on Sunday that Iran needed to address concerns over its ballistic missile programme or risk new sanctions. Iran immediately rejected France's concern over its missile programme as "wrong", the semi-official Fars News agency said.
Hardline media reacted angrily to Le Drian's remarks with headlines like "Rude guest" and "Weapons of mass seduction lands in Tehran", while highlighting Iran's determination to go ahead with its missile programme.
Fars said a group of hardliners gathered at Tehran's International Mehrabad Airport to protest Le Drian's visit.
The 2015 accord between France, Britain, Germany, Russia, China and the United States gave Iran relief from economic sanctions in return for curbs to its nuclear programme, allowing Tehran to talk trade with Europe for the first time in years.
The nuclear deal that was pragmatist President Hassan Rouhani's headline achievement has failed to bring the immediate economic benefits that many expected.
That has slowed down Rouhani's efforts to engage with the West, opposed by influential allies of Iran's top authority Supreme Leader Ayatollah Ali Khamenei who remain uneasy about Iran's efforts to court its old enemies.
France has been quick to restore trade ties. Planemaker Airbus, oil major Total and automobile manufacturers Peugeot and Renault have signed deals, all of which could be at risk if Trump walks out of the accord.
In an effort to keep him on board, French President Emmanuel Macron has criticised Iran's ballistics programme and raised the possibility of new sanctions.
On the eve of Le Drian's visit, he told Rouhani France expects Iran to make a "constructive contribution" to solving crises in the Middle East, Macron's office said on Sunday.
Tehran supports Syrian President Bashar al-Assad against rebels, including groups backed by the West, and backs Israel's enemy Hezbollah in Lebanon.
The two presidents agreed in their phone call to work together in the coming days with the United Nations, the Syrian government and other countries involved to improve the situation for civilians and make a ceasefire effective, Paris said.
France has urged Washington to see the nuclear deal separately from Iran's regional activities and its missile programme, and Le Drian will stress Macron's commitment to the nuclear accord, especially as Iran is respecting its terms, French officials said.
Le Drian is due to meet Rouhani and Foreign Minister Mohammad Javad Zarif as well as officials close to Khamenei, including Ali Shamkhani, secretary of the Supreme National Security Council.
Khamenei said on March 1 that Iran would keep supporting Assad's war effort and a Foreign Ministry spokesman on Sunday rejected Macron's comments about Iran's missile programme, insisting its "defensive missile work" would continue.
An official close to Rouhani said Iran "has always been open to talks and to resolve issues through diplomacy ... but this does not mean we will yield to unjust pressure over our inevitable rights, whether defensive or anything else."
While France says Iran is sticking to the terms of the nuclear deal, it may not be respecting part of U.N. resolution 2231 that calls on it to refrain from work on ballistic missiles designed to carry nuclear warheads.
The resolution enshrines the nuclear deal, which itself makes no explicit reference to the ballistics programme, but it is unclear whether the wording binds Tehran to an obligatory commitment on missiles.
"On the ballistics, the Iranian programme is not compatible with 2231 and we have a particular concern on the transfer of know-how of ballistic capacity to regional actors and by that we mean Hezbollah," said the diplomatic source.
Iran has repeatedly said its missile programme is purely defensive and not in violation of the U.N. resolution.
A second French diplomat said: "While our concerns aren't directly linked to the nuclear deal, it's important we make progress on these other subjects because otherwise Trump risks killing the deal."
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