Negotiations to revive the Iran nuclear deal have entered a "critical" stage during which some key issues still need to be resolved, Iran’s Foreign Minister, Hossein Amir-Abdollahian, said on Wednesday.

Iran has gradually scaled back its compliance with the 2015 nuclear deal it signed with world powers in response to former US President Donald Trump’s withdrawal from the agreement in May of 2018.

It has held several rounds of indirect negotiations with the Biden administration on a possible return to the deal.

Amir-Abdollahian said on Wednesday that the negotiations had "reached a critical and important stage", according to the AFP news agency.

"We hope that some sensitive and important issues remaining in the negotiations will be resolved in the coming days with realism from the Western side," he was quoted as having said at a joint press conference with his Oman counterpart Sayyid Badr al-Busaidi.

Amir-Abdollahian said he was "optimistic" about a deal, while insisting Iran would not give up its "red lines" in the negotiations. He did not elaborate.

A senior European Union official recently said that a US-Iranian deal to revive Iran's 2015 nuclear agreement was close but success depended on the political will of those involved.

French President Emmanuel Macron spoke with his Iranian counterpart Ebrahim Raisi on Saturday and urged him to agree to a deal to revive the 2015 deal.

He added that Iran should seize the opportunity to preserve the Vienna deal and avoid a major crisis, the French presidency statement said.