The Western nationals held in Iran
In the latest development, Frenchman Benjamin Briere -- the only one of those known to be held who does not also have an Iranian passport -- is facing a trial for espionage, his lawyer told AFP on Sunday.
Tehran, which does not recognize dual nationality, insists that all those held have been subject to the proper judicial process.
But it has also not ruled out exchanges for prisoners held in the West. Yet so far there has been no concrete indication of a deal accompanying ongoing talks on the Iranian nuclear drive.
Here are the foreign nationals imprisoned, under house arrest, or unable to leave Iran in cases confirmed by the Iranian authorities, foreign governments, or rights activists.
Supporters say they are innocent and being held as pawns in a political game in which they play no part. Activists also fear there have been more cases yet to be confirmed.
Iranian-American businessman Siamak Namazi has been in prison since his arrest in October 2015 and has now been held for over 2,050 days. His father Mohammad Baquer Namazi was arrested in February 2016 when he went to Iran to try to free his son.
They were both sentenced to 10 years in October 2016 on spying charges. Baquer was released on medical leave in 2018 and is serving his sentence under house arrest.
Morad Tahbaz, an Iranian-American who also holds British nationality, was arrested alongside other environmentalists in January 2018 and sentenced to 10 years for "conspiring with America".
Karan Vafadari, an Iranian-American member of the Zoroastrian minority faith, was arrested in June 2016 on allegations of spying and released on bail in July 2018. He was still unable to leave Iran.
Iranian-American venture capitalist Emad Sharqi was sentenced to 10 years in prison on spying charges, Iranian media reported in January, adding he was captured while trying to flee the country.
Iranian-British citizen Nazanin Zaghari-Ratcliffe was arrested in April 2016 after visiting family, and convicted of plotting to overthrow the regime. She completed that sentence and has been at home in Tehran.
She has been given a new one-year jail sentence for "propaganda against the system" and the UK says her treatment amounts to torture.
Anoosheh Ashoori, a retired Iranian-British engineer, was arrested in August 2017 while visiting his mother and jailed for 10 years on charges of spying for Israel, according to his family.
British-Iranian labor rights activist Mehran Raoof was arrested in October 2020 and is being held in solitary confinement, Amnesty International said.
German-Iranian grandmother Nahid Taghavi, 66, was arrested at her Tehran apartment in October 2020 and has since been held at Tehran's Evin prison amid growing concern for her health.
She had been held for months in solitary confinement but is now in the women's wing of Evin and faces a new trial hearing on June 13, according to her family.
Jamshid Sharmahd, an Iranian-German dissident, was captured by Iran in August 2020, reportedly in a neighboring Gulf country, and charged with terrorism over a deadly 2008 bombing. His family has rubbished the accusations.
French-Iranian academic Fariba Adelkhah was detained in June 2019 and in May 2020 sentenced to five years in prison on national security charges. In October, she was moved to house arrest.
Briere was arrested in Iran in May 2020, allegedly while flying a drone and taking photographs in a prohibited area.
His sister has said the charges are "baseless" and that Briere, who is being held in the city of Mashhad, had become a "negotiating tool".
Iranian-Austrian Massud Mossaheb, 74, was detained in January 2019 and jailed for 10 years on charges of spying for Israel and Germany. His family says he contracted Covid-19 over the winter and has expressed fears for his health.
Iranian-Austrian businessman Kamran Ghaderi, 56, was arrested in January 2016 and sentenced for working with hostile states to 10 years in jail after a trial denounced by Amnesty as "grossly unfair".
Iranian academic Ahmadreza Djalali, a resident of Sweden, was arrested during a visit to Iran in April 2016 and sentenced to death in 2017 on charges of spying for Israel's Mossad. He was granted Swedish citizenship while in jail. In December, there were fears his execution was imminent. The hanging was postponed but his family says he remains on death row.
Habib Chaab, an Iranian-Swedish dissident, disappeared during a visit to Turkey in October 2020 and is now in custody in Iran, where he is accused of being a leading figure in an Arab separatist group. The details of how he was detained remain unclear and Sweden said in December it had not been granted consular access.
Abdolrasoul Dorri Esfahani, a Canadian-Iranian and former nuclear negotiator with a background in banking, was in October 2017 given a five-year prison sentence on spying charges.