Iran has sent French-Iranian academic Fariba Adelkhah back to prison from house arrest, her support group said in Paris on Wednesday, in a shock development amid delicate talks on the Iranian nuclear deal.
Ms Adelkhah was sentenced in May 2020 to five years in prison for conspiring against national security, accusations her supporters have denounced as absurd.
She was allowed home in Tehran in October 2020 with an electronic bracelet.
Ms Adelkhah is one of at least a dozen western nationals believed to be held in Iran. Activists say they are being held as hostages at the behest of the Islamic Revolutionary Guard Corps to extract concessions from the West.
With talks continuing in Vienna aimed at salvaging the 2015 nuclear deal between Tehran and world powers, the French Foreign Ministry warned the move would damage bilateral relations and trust.
"It is with great shock and indignation that we have been informed that Fariba Adelkhah ... has been re-imprisoned in the prison of Evin" in Tehran, the committee set up to support her said.
"The Iranian government is cynically using our colleague for external or internal purposes that remain opaque, and that have nothing to do with her activities."
The committee accused the authorities of "deliberately endangering Fariba Adelkhah's health and even her life", pointing to the death this month in Iranian custody of poet Baktash Abtin after he contracted Covid-19.
France's Foreign Minister Jean-Yves Le Drian complained on Tuesday that the pace of talks in Vienna is "too slow", in marked contrast to the more upbeat tone from officials in Tehran.
The French Foreign Ministry expressed "astonishment" at the reimprisonment of Ms Adelkhah, calling for her immediate release and saying the move was made with "no explanation or preliminary warning".
"The decision can only have negative consequences on the relationship between France and Iran and reduce confidence between our two countries," the ministry said.
Also being held in Iran is Frenchman Benjamin Briere. His family say he was an innocent tourist who was detained while travelling in May.
Mr Briere's family announced last month that he had begun a hunger strike to protest against his detention conditions and the lack of evolution in his case.
A specialist in Shiite Islam and a research director at Sciences Po university in Paris, Ms Adelkhah was arrested in June 2019 along with her French colleague and partner, Roland Marchal.
Mr Marchal was released in March 2020 in an apparent prisoner swap after France released Iranian engineer Jalal Rohollahnejad, who faced extradition to the US over accusations that he breached American sanctions against Iran.
Ms Adelkah's support group said she had been imprisoned "on trumped-up charges and without any proper trial".
Nationals of the three European powers involved in the talks on the Iranian nuclear programme – Britain, France and Germany – are among the foreigners being held.
Also on Wednesday, the British Council said its staff member, Iranian citizen Aras Amiri, had returned to the UK after being cleared on appeal of a 10-year jail sentence for "cultural infiltration" in Iran.
The 2015 nuclear deal – agreed to by Iran, the US, China, Russia, Britain, France and Germany – offered Tehran sanctions relief in exchange for curbs on its atomic programme.
But then US president Donald Trump withdrew the US in 2018 and reimposed sanctions, prompting Tehran to begin breaking its commitments.