France on Friday summoned the Iranian ambassador to protest Tehran's holding of three French nationals Paris says are state hostages, the foreign ministry said.
The envoy was told in "the strongest terms our demand for the immediate release of the French nationals who are state hostages of the Islamic Republic of Iran", the foreign ministry said.
Their "situation is intolerable, with undignified detention conditions that, for some, constitute torture under international law", it added.
Teacher Cecile Kohler and her partner Jacques Paris were detained in Iran in May 2022. They are accused of seeking to stir up labour protests, accusations their families vehemently deny.
Kohler and Paris were also subjected to what France condemned as forced confessions broadcast on Iranian TV after their arrest.
Tehran said in November that the couple were being held "in good conditions and in good health".
Iranian Nobel peace prize winner Narges Mohammadi, currently on leave from prison after over three years behind bars, said Wednesday she was "very worried" about Kohler's situation.
She described her conditions as a "true torture".
A third Frenchman, named Olivier, but whose last name has not been made public, has also been held in Iran since 2022.
The foreign ministry's statement came after an Italian journalist, Cecilia Sala, arrested and jailed in Iran since December, was freed and returned to Rome earlier this week.
Her release was the result of "intense work through diplomatic and intelligence channels" by Prime Minister Giorgia Meloni's government, her office said.
The French foreign ministry repeated a warning that French nationals should not go to Iran.
Those currently there "are recommended to leave Iranian territory immediately due to the risk of arrest and arbitrary detention", it said.