The US-Iranian dual nationals include businessmen Siamak Namazi, 51, and Emad Shargi, 58, as well as environmentalist Morad Tahbaz, 67, who has British citizenship.
They had all been jailed at the notorious Evin Prison in Tehran on spying charges.
The identity of the fourth US citizen allowed out of prison has not been made public, while a fifth man was already under house arrest.
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The families of the Americans held in Iran said their loved ones are “hostages” taken captive on false charges and used as bargaining chips by the government.
Namazi, who in 2016 was convicted of espionage-related charges the US has rejected as baseless, has been detained by Iran for more than seven years.
Tahbaz was arrested in 2018 and sentenced to 10 years in prison for “assembly and collusion against Iran’s national security” and working for the US as a spy.
Shargi was convicted of espionage in 2020 and also sentenced to 10 years in prison.
Due to numerous US sanctions on foreign banks that engage in transactions aimed at benefiting Iran, several European countries were reluctant to take part in the transfer of funds that sealed their release.
The US administration hopes the waiver will dispel these concerns, but it may come at a price for the Democrats as their political opponents will cite an unwelcome boost to the Iranian economy.
Republican senator Tom Cotton of Arkansas accused president Biden of “paying ransom to the world’s worst state sponsor of terrorism”, while senator Chuck Grassley of Iowa said it was “ridiculous… to be blackmailed” to finance what he believes is the number one foreign policy of Iran: “Terrorism”.