Negotiators from Europe and Iran returned to their home countries for consultations as talks aimed at renewing the 2015 nuclear deal reached a key juncture point.
Iran's IRNA news agency said on January 15 that the negotiators would return to Vienna in two days but that expert discussions would continue through the weekend.
The landmark deal, which lifted crippling Western economic sanctions in exchange for curbing Tehran's nuclear ambitions, began to unravel in 2018 after U.S. President Donald Trump unilaterally withdrew and reimposed the sanctions.
That led Iran to later start rolling back its commitments and restarting some uranium enrichment activity, pushing the deal, formally known as the Joint Comprehensive Plan of Action, to the verge of complete collapse.
Efforts to revive the deal resumed in mid-2021 but then were suspended for around five months as Iran elected a new, ultraconservative government.
Along with Iran and the United States, other parties to the deal include Britain, China, France, Germany, and Russia.
The main aims of the negotiations are to get the United States to return to the deal and lift its sanctions and for Iran to resume full compliance.
On January 14, the European Union's foreign policy chief, Josep Borrell, said that a deal remained possible and that the talks were advancing in a "better atmosphere" than before Christmas.
A spokesman for Iran’s Foreign Ministry, Saeed Khatibzadeh, said last week that efforts by "all parties" to revive the deal had resulted in "good progress."