Iran has released four Iranian Americans, one of them thought to be Washington Post reporter Jason Rezaian, as it anticipates the likely lifting of international sanctions imposed over its nuclear programme.
Rezaian was convicted of espionage in Iran last year.
Only four people with US citizenship are known to be in detention in Iran.
Iran said they were being swapped for Iranians held in the US but there was no confirmation from Washington.
News of the releases came after Iranian Foreign Minister Javad Zarif predicted that international sanctions against his country would be lifted on Saturday.
He is in Vienna for talks with US Secretary of State John Kerry over Iran’s nuclear deal.
The international nuclear watchdog, the IAEA, is expected to confirm that Iran has scaled back its atomic activities in line with the agreement, to focus exclusively on peaceful atomic purposes.
Billions of dollars of frozen Iranian assets are expected to be released and the sale of Iranian oil on the world market will again be permitted.
Iran nuclear deal: Key details
In addition to Jason Rezaian, the Associated Press has named as US prisoners held in Iran
Former Marine Amir Hekmati of Flint, Michigan
Pastor Saeed Abedini of Boise, Idaho
Siamak Namazi, a businessman and the son of a politician from the shah’s era
The news agency adds that a former FBI agent, Robert Levinson, disappeared in Iran in 2007 while working for the CIA on an unapproved intelligence mission.
The Washington Post said in a report that there had been no official US confirmation of the release.
One Iranian news agency, Fars, named those released as Rezaian, Hekmati and Abedini. It did not give the fourth prisoner’s name.
“Based on an approval of the Supreme National Security Council and the general interests of the Islamic Republic, four Iranian prisoners with dual-nationality were freed today within the framework of a prisoner swap deal,” the office of Tehran prosecutor said.
According to Fars, the US “also freed six Iranian-Americans who were held [on] sanctions-related charges”.
Iran’s press anticipates lifting of sanctions
Many newspapers have hailed “good days ahead” for the economy, but the hardline press has lamented nuclear restrictions, with Vatan-e Emruz declaring closing the Arak reactor amounted to a “nuclear burial”.
Moderate Iran and reformist Mardom Salari feared Saudi Arabia and US Republicans would try to sabotage the deal, the latter predicting that “powerful hands will try to boobytrap this path”.
Meanwhile Conservative Hemayat said the nuclear deal would not “resolve the problem with the village chief” – referring to the US – and hardline Keyhan argued that the deal had not led to a let-up in US “anti-Iranian propaganda”.
What is the nuclear deal?
In July 2015, Iran agreed a landmark nuclear deal with six world powers to limit its sensitive nuclear activities for more than a decade in return for the lifting of crippling sanctions. The US is confident the agreement will prevent Iran from obtaining a nuclear weapon. Iran says it has the right to nuclear energy – and stresses that its nuclear programme is for peaceful purposes only.
When is ‘implementation day’?
Iran will not see the UN, US and EU sanctions lifted until the global nuclear watchdog, the International Atomic Energy Agency (IAEA), certifies that it has fulfilled its commitments under the deal. The precise date of the so-called “implementation day” has not been determined. But Iran says it has met those commitments earlier than expected.
What does Iran stand to gain?
The sanctions have cost Iran more than more than $160bn (£102bn) in oil revenue since 2012 alone. Once they are lifted, the country will be able to resume selling oil on international markets and using the global financial system for trade.
Iran has the fourth largest oil reserves in the world and the energy industry is braced for lower prices. Iran will also be able to access more than $100bn in assets frozen overseas.
Lifting sanctions would unfreeze billions of dollars of assets and allow Iranian oil to be sold internationally.