Western powers warn Iran against 'dangerous' inspections limit

European powers and the United States on Thursday warned Iran it would be "dangerous" to carry out a threatened limit to UN nuclear agency inspections, warning such a move risked wrecking an opportunity to revive a landmark 2015 deal on its atomic drive.

French Foreign Minister Jean-Yves Le Drian hosted his German and British counterparts in Paris, with America's new Secretary of State Antony Blinken joining via videoconference, to discuss how to bring revive a deal left moribund by former president Donald Trump's pullout in 2018.

Analysts say only a small window of opportunity remains to save the deal as Tehran ramps up its nuclear work in retaliation against the reimposition of sanctions that followed the US walkout.

A French diplomatic source, who asked not to be named, said a key step forward was that the United States was prepared to have discussions with Iran for Tehran to return to full compliance with the deal.

But the hugely sensitive diplomatic process risks being derailed by an Iranian threat to restrict some UN nuclear agency inspections by February 21 if the US does not lift the sanctions.

The joint statement urged "Iran to consider the consequences of such grave action, particularly at this time of renewed diplomatic opportunity."

The administration of US President Joe Biden has said it is prepared to rejoin the deal and start lifting sanctions if Iran -- whose economy has been devastated -- returns to full compliance.

But Tehran rejected this precondition, pressing on with increasing nuclear work in retaliation for Trump's so-called "maximum pressure" sanctions policy to weaken the Iranian regime which has had no relations with Washington for four decades.

The statement said Blinken reiterated that if "Iran comes back into strict compliance with its commitments" under the nuclear deal "the United States will do the same and is prepared to engage in discussions with Iran toward that end."

The French diplomatic source acknowledged the deal is being "less implemented than ever" but said there was a now a shared consensus of all parties on the aim of the process.

"The Americans are saying: it must start with a discussion" with the Iranians, said the source.

The United States and Iran have had no diplomatic relations for four decades but they did have contacts concerning the 2015 nuclear deal.

However, the meeting in Paris did not appear to offer any concession to Iran and Iranian Foreign Minister Mohammad Javad Zarif appeared unimpressed.

He tweeted: "Instead of sophistry and putting the onus on Iran, E3/EU must abide by own commitments and demand an end to Trump's legacy of economic terrorism against Iran."

The Joint Comprehensive Plan of Action (JCPOA), signed in Vienna in 2015, was based on Iran accepting safeguards designed to prevent it from developing an atomic bomb, in exchange for a gradual easing of international sanctions.

International Atomic Energy Agency (IAEA) chief Rafael Grossi is to travel to Tehran on Saturday for talks with the Iranian authorities to find a solution for continuing inspections in the country, the agency said.

"Iran's nuclear programme is growing by the day, as the time it would take to enrich enough uranium for a single nuclear weapon shrinks," said Ali Vaez, Iran project director at the International Crisis Group (ICG).

The powers also expressed their concerns over Iran's recent actions to produce both uranium enriched up to 20 per cent and uranium metal.

"These activities have no credible civil justification," the statement said.

German Foreign Minister Heiko Maas said earlier that Iran's recent steps were endangering the prospect of the US returning to the deal, warning that Iran was "playing with fire."

While Iran's policy is ultimately determined by supreme leader Ayatollah Ali Khamenei, Iranian presidential elections in June add another time pressure factor.

Rouhani -- a key advocate of nuclear diplomacy with global powers -- is set to step down after serving the maximum two consecutive terms, and a more hardline figure is likely to replace him.

Vaez said "the seemingly impossible dilemma has a solution" if the two sides were prepared to take "closely synchronised steps".

This would involve Washington revoking Trump's 2018 withdrawal and greenlighting an Iranian request for an emergency IMF loan, while Iran freezes "the most problematic aspects" of its nuclear programme, he said.

Ellie Geranmayeh, senior policy fellow at the European Council on Foreign Relations, said Washington should use this "short window of time" to move to show Iran that the Biden administration "is distancing itself from Trump-era maximum pressure".