Iran has freed four Iranian-Americans under a prisoner swap deal with the United States, Iranian prosecutors announced Saturday, as the chief diplomats from both countries were preparing the launch of a far-reaching nuclear deal in Vienna.
Washington Post reporter Jason Rezaian, taken into custody in July 2014 and convicted on espionage charges last year, was among the prisoners released, the Iranian Fars news agency reported, citing prosecutors.
US Marines veteran Amir Hekmati, a pastor named Saeed Abedini and a man named Nosratollah Khosrawi were named by Iranian media as the three other freed prisoners.
In exchange, seven Iranian citizens were released in the United States, broadcaster CNN quoted US sources as saying.
The release was announced the same day that US Secretary of State John Kerry arrived in Vienna for meetings with Iranian Foreign Minister Mohammad Javad Zarif and EU chief diplomat Federica Mogherini to clarify remaining issues before the planned implementation of a broad nuclear deal with six major powers that will end sanctions against Tehran.
Despite the announced prisoner swap, diplomats said some issues remained to be resolved.
"The devil is in the detail," a diplomatic source said.
Iran finalized an agreement with the United States, Britain, France, Germany, Russia and China in July to curb Tehran's nuclear programme and prevent it from making nuclear weapons in return for sanctions relief.
The involved countries were still waiting for a final report by the Vienna-based International Atomic Energy Agency (IAEA) on Saturday to confirm that Tehran has fulfilled the required nuclear steps.
This confirmation will oblige the EU and US to immediately lift sanctions including an embargo on Iranian oil, according the July 14 deal.
Iran had agreed in July that it would dismantle thousands of uranium enrichment centrifuges, reduce its stocks of enriched uranium from 12 tons to hundreds of kilograms and to pour concrete into its plutonium-producing Arak reactor.
The downsizing of Iran's civilian nuclear programme, along with intrusive IAEA inspections in the coming years, are meant to ensure that Iran cannot make nuclear weapons.
Iran's regional foes Israel and Saudi Arabia are worried that the nuclear agreement could boost Iran's clout in the region, and that thawing ties between long-time enemies Washington and Tehran could decrease their own status.
The implementation of the nuclear deal was set to come 13 years after revelations that Tehran had secretly built nuclear facilities and had dabbled in nuclear weapons research.