Tehran has freed Washington Post reporter Jason Rezaian and three other Iranian-American dual nationals in a prisoner swap deal that also saw Washington release seven Iranian nationals.
Rezaian, the Post's Tehran bureau chief, had been imprisoned in Iran for more than a year on espionage charges. He and The Washington Post have repeatedly denied the charges, saying he was arrested as a bargaining chip in a larger political game.
Also released by Iran were pastor Saeed Abedini, an Iranian-American in jail for three years after being convicted of undermining national security, and former US Marine Amir Hekmati, who is serving 10 years for cooperating with hostile governments.
A U.S. official identified the fourth freed prisoner as Nosratollah Khosravi-Roodsari. There have been mixed reports in the Iranian media about the identity of the fourth person, with Iran's IRNA news agency earlier naming him as Iranian-American businessman Siamak Namazi.
Reuters quotes U.S. officials as saying Iran also has released a fifth person separately from the prisoner exchange, an American student named Matthew Trevithick.
U.S. officials confirmed that the United States offered clemency to seven Iranians, six of whom are dual U.S.-Iranian citizens, who had been convicted or are awaiting trial in the United States.
Western media have named the Iranians as Nader Modanlo, Bahram Mechanic, Khosrow Afghahi, Arash Ghahreman, Tooraj Faridi, Nima Golestaneh, and Ali Sabouni.
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The deal also saw Washington dismiss charges against 14 other Iranians.
There are a dozen Iranians imprisoned or facing charges in the United States on sanctions-busting charges, according to a recent Reuters review of cases. U.S. Prosecutors say they violated economic sanctions against Iran by supplying technology that could have been used to bolster its military and nuclear programs.
The prisoner swap came as Iran and world powers led by the United States are expected on January 16 to finally implement July's nuclear deal, which will lift international sanctions imposed on the Islamic republic.
The lifting of sanctions is expected to come as the UN's nuclear watchdog agency says Tehran has fulfilled its obligations to restrict its nuclear programs under the deal.