The United States and France on Friday warned Iran that time is running out to return to a nuclear deal, voicing fear that Tehran's sensitive atomic activities could advance if talks drag on.
On the first high-level visit to Paris by President Joe Biden's administration, Secretary of State Antony Blinken and his French hosts saluted a new spirit of cooperation after four years of turbulence under Donald Trump.
But the two sides said that one key Biden promise -- to return to the 2015 Iran accord that was trashed by Trump -- is at risk if the clerical regime does not make concessions during talks that have been going on for more than two months in Vienna.
Blinken warned that the United States still has "serious differences" with Iran, which has kept negotiating since last week's presidential election won by hardliner Ebrahim Raisi.
"There will come a point, yes, where it will be very hard to return back to the standards set by the JCPOA," Blinken told reporters, using the acronym for the accord's formal name.
"We haven't reached that point -- I can't put a date on it -- but it's something that we're conscious of."
Blinken warned that if Iran "continues to spin ever more sophisticated centrifuges" and steps up uranium enrichment, it will bring nearer the "breakout" time at which it will be dangerously close to the ability to develop a nuclear bomb.
But Blinken said that Biden still supports a return to the accord, under which Iran had drastically scaled back its nuclear work until Trump withdrew in 2018 and imposed crippling sanctions.
"We have a national interest in trying to put the nuclear problem back in the box that it was in the JCPOA," Blinken said.
- Stalling as strategy? -
France -- which like Britain, Germany, Russia and China had stayed in the 2015 accord despite pressure from Trump -- also ramped up pressure on Iran to move ahead.
"We expect the Iranian authorities to take the final decisions -- no doubt difficult ones -- which will allow the negotiations to be concluded," Foreign Minister Jean-Yves Le Drian said at the joint news conference with Blinken.
Iranian foreign ministry spokesman Saeed Khatibzadeh said in a statement in response: "The opposing sides are the ones who must take the decisions."
The UN nuclear watchdog said Friday it had received no reply from Tehran over the possible extension of a temporary agreement covering inspections at Iranian nuclear facilities which expired on Thursday.
Under that deal, which had allowed for some IAEA inspections to continue after Iran limited access to sites in February, Tehran pledged to keep recordings "of some activities and monitoring equipment" and hand them over to the IAEA as and when US sanctions are lifted.
But Iran's envoy to the IAEA said on Twitter that the data recording was "a political decision" to facilitate the political talks and "shouldn't be considered as obligation".
Talks have stalled in part over Iran's insistence on the lifting of all sanctions, pointing to the promises of economic relief under the accord.
The Biden administration says it is ready to lift economic measures related to nuclear work as laid out by the JCPOA -- but that it will keep other sanctions, including over human rights and Iran's support to militant movements in the Arab world.
Some experts believe that Iran had been waiting for the election of Raisi, whose hardline approach is backed by Supreme Leader Ayatollah Ali Khamenei, the ultimate arbiter of the Islamic republic's foreign policy.
Analysts have said Iran could strike a deal before Raisi takes office in August -- letting him take the credit for the expected economic boost but blame outgoing president Hassan Rouhani, a moderate who championed a better relationship with the West, if the situation deteriorates.
- 'Welcome home' -
Blinken, who was raised in Paris, hailed the alliance with France and sprinkled his remarks with fluent French, in a sharp change of tone after the sometimes abrasive "America First" approach of the Trump administration.
"I would even be tempted to say, welcome home!" Le Drian said as he welcomed Blinken in an ornate room of the Quai d'Orsay, the French foreign ministry.
Blinken later met French President Emmanuel Macron at the Elysee Palace. The State Department said they looked for common ground on the challenges of Russia and China, crises in Lebanon and Ethiopia and the fight against Islamic State extremists in the Sahel.
Blinken is on a European tour that also took him to Germany and will continue in Italy, just after Biden visited the continent.
The Biden administration has looked to show unity with Europe as it looks to the rise of an increasingly assertive China as its primary global challenge.