Reviving Iran's nuclear deal under US President-elect Joe Biden would require striking a new agreement setting out how Iran's breaches should be reversed, UN atomic watchdog chief Rafael Grossi said.
Iran has breached many of the deal's limits on its nuclear activities in response to US President Donald Trump's withdrawal from the deal and the reimposition of US sanctions against Tehran that the deal lifted. Tehran often says it can quickly reverse its breaches if US sanctions are removed.
Biden, who takes office on Jan. 20, has said the United States will rejoin the deal "if Iran resumes strict compliance" with the agreement that imposed strict curbs on its nuclear activities in return for the lifting of sanctions.
In an interview with Reuters, Grossi, who heads the International Atomic Energy Agency that polices the deal, said there had been too many breaches for the agreement to simply fall back into place.
"I cannot imagine that they are going simply to say, 'We are back to square one' because square one is no longer there," Grossi said at theInternational Atomic Energy Agency (IAEA) headquarters.
"There is more (nuclear) material, ... there is more activity, there are more centrifuges, and more are being announced. So what happens with all this? This is the question for them at the political level to decide," said Grossi, an Argentine who took office as IAEA director general a year ago.
Asked if that meant there would have to be a 'deal within the deal', he said: "Oh yes, oh yes. Undoubtedly.
"It is clear that there will have to be a protocol or an agreement or an understanding or some ancillary document which will stipulate clearly what we do," he said.
Iran's stockpile of enriched uranium is more than 2.4 tonnes, 12 times the cap set by the deal, though still far below the more than eight tonnes Iran had before signing it. Iran has been enriching uranium up to 4.5% purity, above the deal's 3.67% limit though below the 20% it achieved before the deal.
Iran is enriching uranium in places where it is not allowed under the deal, such as at Fordow, a site dug into a mountain. More recently it has started enriching with advanced centrifuges at its underground plant at Natanz, where the deal says it can use only first-generation IR-1 machines.
"What I see is that we're moving full circle back to December 2015," Grossi said, referring to the month before the deal's restrictions were put in place, after which large amounts of material and equipment were swiftly removed.
"If they want to do it (comply), they could do it pretty fast. But for all of those things we had a charted course," he said.
Iran's activities have increasingly worried some of the deal's other remaining parties, including Russia, which has urged Tehran to act responsibly, and France, Britain and Germany, which have desperately tried to keep the accord alive.
When asked whether it believed a new protocol would be needed, France's foreign ministry stressed that Iran's actions were becoming a serious problem.
"Their consequences, especially in the area of enrichment, are serious. They call into question the advantages of this agreement in terms of non-proliferation," deputy spokesman Francois Delmas said.
"Iran must therefore return without delay to full compliance with the agreement and refrain from any new action that would call into question its sustainability."