The Islamic republic also threatened to abandon more commitments unless a solution is found with parties to the 2015 agreement.

The move to start enriching uranium above the agreed maximum purification level of 3.67 percent comes despite opposition from the European Union and the United States, which has quit the deal.

President Hassan Rouhani's order to exceed the threshold would be implemented "in a few hours" after the last technical details were sorted, Iran's Atomic Energy Organisation spokesman Behrouz Kamalvandi said live on state television.

Rouhani initially flagged Tehran's intentions on May 8, exactly a year on from US President Donald Trump unilaterally abandoning the multilateral deal.

He has said the move is in response to a failure by remaining state signatories to keep their promise to help Iran work around biting sanctions reimposed by the US in the second half of last year.

Deputy Foreign Minister Abbas Araghchi on Sunday singled out Iran's declining oil sales as one of the main issues that needed to be solved, or Tehran would further step back from its commitments.

"We hope we can reach a solution otherwise after 60 days we will take the third step as well," he said, without specifying what the further measures would involve.

French President Emmanuel Macron told Rouhani of his "strong concern" over the risk of weakening the nuclear agreement and the consequences that would follow during a telephone call Saturday, according to a statement from the Elysee Palace.

However, the two leaders agreed to "explore by July 15 the conditions for a resumption of dialogue between all parties", the statement said, adding that Macron would consult with Iranian authorities and international partners to bring about the "necessary de-escalation" of the situation over the coming days.

It is not yet clear how far the Islamic republic will boost enrichment.

But a top advisor to Iran's Supreme Leader Ayatollah Ali Khamenei hinted on Friday it could reach five percent.

- 'Extremely concerned' -

The 2015 deal was reached between Iran and six world powers -- Britain, China, France, Germany, the United States and Russia -- and saw Tehran agree to drastically scale down its nuclear programme in exchange for sanctions relief.

Washington began reimposing sanctions in August 2018 and has targeted crucial sectors including oil exports and the banking system, fuelling a deep recession.

The 3.67 percent enrichment limit set in the agreement is sufficient for power generation but far below the more than 90 percent level required for a nuclear warhead.

Rouhani has stressed that Iran's action would be reversed if the other parties provided relief from the US sanctions, insisting his country's policies are not meant to "hurt (the deal), but to preserve" it.

France has warned Tehran that it would "gain nothing" by leaving the deal and has said "challenging the agreement would only increase tensions" in the Middle East.

Iran says that it is not violating the deal, citing terms of the agreement allowing one side to temporarily abandon some of commitments if it deems the other side is not respecting its part of the accord.

The diplomatic chiefs of Britain, France, Germany and the EU have said they were "extremely concerned".

Trump, meanwhile, has warned Iran that it is "playing with fire".

- 'Strategic patience' -

Iran says it exercised "strategic patience" for a year after the US withdrawal, waiting for the other signatories to make good on promised economic benefits.

But on May 8, Tehran announced it would no longer respect two key limits -- a 1.3-ton maximum for heavy water reserves and a cap of 300 kilogrammes on its low-enriched uranium stockpile.

The IAEA has in recent days confirmed that Iran has breached the limit of 300 kilogrammes and has scheduled a special meeting on Iran's nuclear programme for July 10.

Also on May 8, Tehran gave a 60-day ultimatum -- a deadline that expires Sunday -- to deal partners to help it circumvent US sanctions, on pain of abandoning two more nuclear commitments.

One was the enrichment cap. The other was a freeze on construction of a heavy water reactor.

Rouhani referenced the reactor Wednesday, telling critical powers "according to you, (this) is dangerous and can produce plutonium".

Europe has sought to salvage the nuclear deal by setting up a payment mechanism known as INSTEX which is meant to help Iran skirt the US sanctions.

But Rouhani has dismissed the mechanism as "hollow" because it has not facilitated purchases of Iranian oil.