US Secretary of State Antony Blinken has hailed the confirmation of Iran Special Envoy Robert Malley, who stepped into the role on January 28. In a tweet Sunday, Mr Blinken said Mr Malley was "off to a great start," despite a looming escalation in the nuclear crisis.
Mr Malley, who is known as one of the architects of the original nuclear deal with Iran in 2015, was appointed as part of a new strategy by US President Joe Biden to return to diplomacy. But Washington has also made it clear that the US will not be rushed into re-entering the nuclear deal, which was later abandoned by Donald Trump.
Nonetheless, a series of dates is approaching that will force the new US administration to show its hand.
The Biden administration has repeatedly said it will return to full compliance with the deal, formally known as the Joint Comprehensive Agreement Plan of Action, when Iran does.
In other words, Mr Biden will lift sanctions imposed by Mr Trump only after the clerical regime reverses nuclear steps it took to protest those sanctions.
Iran, probably mindful of the widespread hostility it faces in Washington, wants to ensure an end to sanctions before it backs down on steps away from the nuclear commitments, which included enriching uranium beyond agreed limits.
A key date comes on February 21 when Iran, under a law passed in December by the conservative-led parliament, is set to stop allowing intrusive inspections by the International Atomic Energy Agency unless US sanctions are eased.
Kelsey Davenport, director for nonproliferation policy at the Arms Control Association in Washington, said Iran could quickly undo most steps, such as uranium enrichment.
"But the steps that are coming, I think, do pose a more significant risk and are more difficult to reverse," she said.
While Iran has stopped short of threatening to expel IAEA inspectors, Ms Davenport said she worried that any loss of access would fuel speculation that Tehran is engaged in illegal activities.
The risk "underscores the importance of restoring full compliance with the JCPOA before Iran takes these steps and develops this new knowledge," she said.
Another key date is in June, when Iran will hold elections that could bring to power a hardline successor to President Hassan Rouhani.
Mr Rouhani bet on engagement with the West when Barack Obama was president, only for tension to soar under Mr Trump.
With February 21 fast approaching, "it is imperative that diplomacy happens", a former EU diplomat said.
"The next 10 days will be important to give us an idea of what is occurring and how successful it will be" in persuading Iran to step back, the diplomat said.
"The entire issue is to make sure that the threshold is not crossed on that date," another European diplomat said.
The diplomat said that position was shared by Russia and China, which are also signatories to the JCPOA but enjoy far closer relations with Iran than western powers.
Jon Wolfsthal, who advised Mr Biden when he was Obama's vice president, said the United States and Iran, along with other JCPOA nations, could issue a statement before February 21 "that would show their mutual intent to return to full compliance."
But while action would be best as soon as possible, he doubted that decision-making would fundamentally change after the elections in Iran, where Supreme Leader Ayatollah Ali Khamenei has final say.
"I don't think the United States is going to say, Oh, we have to give away everything we have to do everything, because after June it's impossible," said Mr Wolfsthal, who is now at Global Zero, a pressure group against nuclear weapons.
On Friday, State Department spokesman Ned Price stressed the US was "not looking at any particular deadline" when asked about February 21.
The Biden administration has named a special envoy on Iran, Rob Malley, who is one of the architects of the JCPOA.
Officially his first task has been co-ordination with Europe and he will only afterwards revive the US dialogue with Iran that ended under Mr Trump.
But one former adviser to Mr Obama, speaking on condition of anonymity, said: "I suspect that US officials have already engaged with Iranian officials in some number of ways."
Thomas Countryman, who was a top arms control official in the Obama administration, said Mr Biden could immediately lift some sanctions to show good faith.
With help from Europe, the US and Iran could also lay out the steps they will take, he said.
"Because of the domestic political situation in both countries, I think they've got to find a way to say 'We did not give in to pressure'," Mr Countryman said.
Iranian Foreign Minister Javad Zarif has himself called for EU foreign policy chief Josep Borrell to "choreograph" action between Washington and Tehran.
Observers say other steps the US could take include offering Iran Covid-19 vaccines or dropping Trump-era objections to the International Monetary Fund lending Tehran money to fight the pandemic.
