A deal between the US and Iran will see Washington unfreeze $6 billion of Iranian funds that will then be sent to Qatar and made available for Tehran.
In return, five US-Iranian dual citizens are expected to be freed and leave Iran, while a similar number of Iranian prisoners held in the US with also be released.
Here is what we know so far about the five detainees, four of whom were released from Evin prison in August and placed them under house arrest before their repatriation to the US.
Siamak Namazi
Siamak Namazi, 51, an Iranian-American businessman, has been held in Tehran on espionage charges since October 2015.
The oil company executive was convicted of collaborating with a hostile government, the US, in 2016 and has since become the longest-serving US-Iranian prisoner held in Iran.
Tehran resisted repeated demands by successive US administrations for his release.
His father, Baquer Namazi, was arrested in 2016 after he flew into Iran to visit his son in a Tehran prison.
The elder Namazi was detained for years and was only allowed to leave Iran in October 2022. He went to the UAE for medical treatment.
Emad Shargi
Emad Shargi, 59, a businessman from Washington, DC, was jailed in October 2018 on what the US government described as “bogus” espionage charges.
According to an NPR interview with his wife, Bahareh Shargi, Mr Shargi was born in Iran and moved to the US when he was young, eventually becoming a citizen.
Iran does not recognise dual nationalities so Mr Shargi was deprived of regular US consular access.
The wife told NPR that she and her husband had decided to live in a family home in Tehran after their children went to university. He was arrested in April 2018 and taken to Iran's notorious Evin prison.
Morad Tahbaz
Environmentalist Morad Tahbaz, 67, was arrested in his country of birth in January 2018 during a crackdown on environmental activists.
Tehran accused him and seven other conservationists of collecting classified material about Iran’s strategic areas, under the guise of environmental work.
His Canadian-Iranian colleague, Kavous Seyed-Emami, died in custody a few weeks later in unexplained circumstances.
Two other detainees
Reuters reported that the identities of the fourth and fifth Americans, one of whom according to sources is a woman, have not been disclosed.
It was not immediately clear which Iranian prisoners being held in the US would in turn, would be swapped.
Robert Levinson
There has been no word on the fate of Robert Levinson, who was taken into custody by Iran in 2007.
Mr Levinson disappeared from Iran’s Kish Island and for years, US officials would only say that the meticulous FBI investigator credited with busting Russian and Italian mobsters was working for a private company on his trip.
In December 2013, it was revealed that he had been on a mission for CIA analysts who had no authority to run spy operations.
The US government in 2020 reported that he had probably died while in Iranian custody.
