“It is positive that the Americans appear willing to tolerate Iranian enrichment within clearly set boundaries,“ Fidan, who has been involved in talks with both Washington and Tehran, told the FT.

“The Iranians now recognise that they need to reach a deal with the Americans, and the Americans understand that the Iranians have certain limits. It’s pointless to try to force them.”

Washington has until now demanded Iran relinquish its stockpile of uranium enriched to up to 60% fissile purity, a small step away from the 90% that is considered weapons-grade.

Iranian President Masoud Pezeshkian has said Iran would continue to demand the lifting of financial sanctions and insist on its nuclear rights, including enrichment.

Fidan told the FT he believed Tehran “genuinely wants to reach a real agreement” and would accept restrictions on enrichment levels and a strict inspection regime, as it did in the 2015 agreement with the US and others.

US and Iranian diplomats held in Oman last week in an effort to revive diplomacy, after President Donald Trump positioned a naval flotilla in the region, raising fears of new military action.

Trump on Tuesday said he was considering sending a second aircraft carrier to the Middle East, even as Washington and Tehran prepared to resume negotiations.

The Turkish foreign minister, however, cautioned that broadening the Iran-US talks to ballistic missiles would bring “nothing but another war.”

The US State Department and the White House did not respond to a request for comment outside regular business hours.