"There is still lots to work out, it's still very fragile," Le Drian told journalists in Paris regarding 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 the accord last year.

Trump later re-imposed harsh sanctions that have pummelled the Iranian economy, hoping a strategy of "maximum pressure" would force Tehran to accept a stricter accord to curtail its nuclear ambitions.

But Trump surprised many at the G7 summit in Biarritz, France, last month by saying he would be prepared to meet his Iranian counterpart.

That came after the summit host, President Emmanuel Macron, invited Iranian 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 were now focused on a possible guaranteed credit line for Tehran in exchange for oil, in exchange for Iran promising to adhere to the terms of 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.

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