Iran's chief negotiator will fly back to Vienna on Sunday evening following consultations in Tehran, state media said, as talks to revive the 2015 nuclear deal reached a critical stage, APA's Tehran Bureau reports.
Ali Bagheri "will return to Vienna this evening with clear instructions to pursue the negotiations with the aim of solving problems in order to reach an agreement."
The talks to restore the agreement, known formally as the Joint Comprehensive Plan of Action, involve Iran as well as Britain, China, France, Germany, and Russia directly, and the United States indirectly.
Bagheri left Vienna on Wednesday night, but negotiations have continued on the level of experts.
Remaining parties to the deal, excluding Iran, met Sunday with the US delegation in Vienna, Russia's envoy Mikhail Ulyanov said.
"We are waiting for the return of the Iranian chief negotiator... to finalize the agreement on restoration of JCPOA," Ulyanov tweeted.
In recent days, all sides have signaled progress in the talks, saying they have reached a critical stage.
"We usually have to be realistic in our conversations, rather than optimistic or pessimistic," Iranian Foreign Ministry spokesman Saeed Khatibzadeh told state TV on Sunday.
"Vienna negotiations have reached the point of serious political decisions by the United States and Western parties."