Secretary of State Antony Blinken told European allies that the US is prepared to talk to Iran about both countries returning to compliance with a 2015 deal that aims to stop Tehran from developing a nuclear weapon.
European powers and the United States have 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 new US 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.
READ MORE: Iran: EU mediation likely to overcome nuclear deal impasse with US
The joint statement urged "Iran to consider the consequences of such grave action, particularly at this time of renewed diplomatic opportunity."
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 percent and uranium metal.
Enrichment of 20 percent is well above the deal's 3.67 percent limit, though still well bel ow the 90 percent that is weapons grade.
"These activities have no credible civil justification," the statement said.
READ MORE: Iran nuclear deal parties seek to patch fragile accord
US to rejoin deal
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.
READ MORE: If the Iran nuclear deal can be saved, there is no time left to waste
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.
READ MORE: Qatar seeks mediation between US and Iran on teetering 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 onus on Iran, E3/EU must abide by own commitments and demand an end to Trump's legacy of economic terrorism against Iran."
"Our remedial measures are a response to US/E3 violations. Remove the cause if you fear the effect," he continued. "We'll follow ACTION w/ (with) action."
The Joint Comprehensive Plan of Action (JCPOA), signed in Vienna in 2015, was based on Iran accepting safeguards designed to prevent it developing an atomic bomb, in exchange for a gradual easing of international sanctions.
READ MORE: Iran will expel UN nuclear inspectors unless sanctions are lifted
'Playing with fire'
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."
Iran’s threats are “very worrying," British Foreign Secretary Dominic Raab said, stressing the need "to re-engage diplomatically in order to restrain Iran, but also bring it back into compliance.”
The diplomats also expressed concern about human rights violations in Iran and its ballistic missile program.
German Chancellor Angela Merkel and the president of the European Council spoke with Iranian President Hassan Rouhani this week to try to end the diplomatic standoff.
READ MORE: Russia, Iran urge US to rescue nuclear deal
'Solution for dilemma'
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 green-lighting 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."
READ MORE: Meet the Biden administration’s Iran envoy, an unpopular man in Israel