Iranian-French academic Fariba Adelkhah was released from Iran’s Evin prison, France said on Friday, but it was unclear what the conditions of her release were.
Ms Adelkhah has been in prison since Iranian authorities arrested her in 2019 during a visit.
She is one of seven French nationals detained in Iran, a factor that has worsened relations between Paris and Tehran in recent months."
"It is essential that all of Ms Fariba Adelkhah's freedoms are restored, including returning to France if she wishes," the French foreign ministry said in a statement.
Ms Adelkhah's lawyer said it was still unclear how much longer she will have to stay in Iran before returning to France.
“She was freed last night and is now at her home,” Hojjat Kermani told Reuters.
“Legally, her file is considered completed, and legally there should be no problem to leave the country, but this issue has to be reviewed. So ... it is not clear how long it will take.”
Iranian authorities sentenced Ms Adelkhah in 2020 to five years in prison on national security charges.
They moved her to house arrest later but in January she returned to jail. Ms Adelkhah has denied the charges.
France has called them "politically motivated" and repeatedly called for the release of Ms Adelkhah, a researcher affiliated with Paris’ prestigious Sciences Po university.
In recent years, Iran's elite Revolutionary Guards have arrested dozens of dual nationals and foreigners, mostly on charges related to espionage and security.
Rights groups have accused Iran of trying to extract concessions from other countries through such arrests.
Iran, which does not recognise dual nationality, denies taking prisoners to gain diplomatic leverage.
"France reiterates its demand that all French nationals arbitrarily detained in Iran are released immediately and without conditions," the foreign ministry added.