"There is still lots to work out, it's still very fragile," Le Drian told journalists in Paris about the talks between Tehran and three European countries -- France, Britain and Germany -- to keep the nuclear deal alive after US President Donald Trump pulled out of it last year.

Trump later reimposed harsh sanctions that have pummelled the Iranian economy, prompting a defiant Tehran to ramp up its uranium enrichment to levels in breach of the 2015 deal.

Both sides appeared in more conciliatory form last month at the G7 in France, where Trump caused surprise by saying he would be prepared to meet his Iranian counterpart.

That came after the summit host, President Emmanuel Macron, invited Iran's Foreign Minister Mohammad Javad Zarif to attend the talks, though he did not meet with Trump directly.

"The president sensed that president Trump was open to softening the strategy of maximum pressure, to find a path that could allow a deal to be reached," Le Drian said.

He said talks on Monday in Paris with Iranian officials focused on a possible guaranteed credit line for Tehran in exchange for oil, conditioned on Iran's renewed compliance with the 2015 deal.

Tehran would also have to commit to easing geopolitical tensions in the Gulf region, and participate in Middle East talks on improving regional security, Le Drian said.

"That all supposes of course that President Trump allows waivers on some points" of the new US sanctions on Iran, he added.

A conservative Iranian lawmaker was quoted by media reports at the weekend as saying that Macron had proposed a $15-billion-euro credit line, a figure that French officials have not confirmed.

- 'It should work' -

Earlier Tuesday, Iran's President Hassan Rouhani ruled out holding any direct talks with the United States, and warned that Tehran would stop complying with other elements of the 2015 accord if the talks with European nations yield no results by Thursday.

As part of their efforts to keep the nuclear deal alive, France, Germany and Britain have set up a mechanism called INSTEX that would allow continued trade with Iran despite the US sanctions.

"We have to finish the work on INSTEX... normally it should work," Le Drian said.

The subject could be on the table when French Finance Minister Bruno Le Maire meets his US counterpart Steven Mnuchin in Washington on Tuesday.

Macron and Rouhani have held a series of phone calls in recent weeks aimed at salvaging the nuclear deal.