Iranian President Hassan ­Rouhani Tuesday told the US to "take the first step" by lifting all sanctions against Iran, dampening down the likelihood of meeting US counterpart Donald Trump.

Iranian Foreign Minister ­Mohammad Javad Zarif said the prospects for such a meeting were "unimaginable" ­without Washington ­rejoining the nuclear deal with Tehran, two days after he made a ­surprise trip to Biarritz for talks on the sidelines of the G7 summit.

Trump had said on Monday he was ready to meet with the Iranian president within weeks, in a potential breakthrough reached during the summit in the French seaside resort.

Iran's economy has been battered by US sanctions imposed since Trump in May last year unilaterally withdrew from a landmark 2015 nuclear deal between the Islamic republic and world powers.

"The step is to retreat from sanctions. You must retreat from all illegal, unjust and wrong sanctions against the nation of Iran," Rouhani said in a speech aired live on state television.

"The key for positive change is in the hands of Washington," he said, because Iran had already ruled out ever doing what worries the US the most - building an atomic bomb.

"If honestly this is your only concern, this concern has already been removed" through a fatwa issued by supreme leader Ayatollah Ali Khamenei, said Rouhani.

"We don't [intend to] make an atomic bomb... our military doctrine is based on conventional arms," said the Iranian president.

Khamenei issued a fatwa against nuclear weapons in 2003 and has reiterated it ­several times since.

"So take the first step. Without this step, this lock will not be unlocked," Rouhani said at an event in Tehran.

In Biarritz, French President Emmanuel Macron had said the "conditions for a meeting" between Trump and Rouhani "in the next few weeks" had been created through intensive diplomacy and consultations.

Trump, speaking at the final news conference of the G7 summit, said he "would certainly agree to that."

He added that the timeline proposed by Macron was realistic.

Trump was equally confident that Rouhani would be in favor. 

"I think he's going to want to meet. I think Iran wants to get this situation straightened out," he added.

But Zarif said on Tuesday that he had made it known during the G7 summit that a meeting between Rouhani and Trump would be highly improbable even if the US returned to the nuclear deal.