France has confirmed that a second French academic is being detained in Iran, condemning what it described as "an unacceptable situation."
Roland Marchal was arrested in June, at the same time as Fariba Adelkhah, a dual French and Iranian citizen, France's Foreign Ministry said on October 16.
Both are senior researchers from Paris's prestigious Sciences Po university. It was previously known that Adelkhah had been taken into custody, but the ministry had not confirmed Marchal had been detained as well.
It was not clear what crimes the academics are accused of.
French Foreign Ministry spokeswoman Agnes von der Muhll urged the Iranian authorities to "show transparency in this dossier and act without delay to end the unacceptable situation."
Marchal's arrest had not been made public as the French authorities were seeking to work discreetly for his release, reports said.
Marchal has received consular visits and has a lawyer, von der Muhll said.
In an e-mail sent to students, Sciences Po's management denounced his "arbitrary, scandalous, and revolting" arrest.
Marchal and Adelkhah are said to be held in Tehran's Evin prison.
French newspaper Le Figaro and Reuters first reported Marchal's detention on October 15.
Tehran has called the detention of Adelkhah, a 60-year-old anthropologist, an internal affair, and refused to offer her consular access, insisting that it does not recognize dual nationality for its citizens.
On October 14, Iran's Islamic Revolutionary Guards Corps (IRGC) announced it had captured a third person linked to France, exiled opposition activist Roohollah Zam, claiming he was being directed and supported by intelligence officials from France, the United States, and Israel.
The IRGC did not make clear how Zam, based in France, was apprehended, saying only that he was first "guided into" Iran.
The French Foreign Ministry said that Zam was a refugee with French residence papers, left France on October 11, and was arrested abroad. https://www.diplomatie.gouv.fr/en/country-files/iran/events/article/iran-situation-of-ruhollah-zam-q-a-from-the-press-briefing-16-oct-19
The ministry said it had no specific information concerning the circumstances of Zam's arrest, adding that the French authorities "strongly condemn" the move.
Iran's state television has showed footage of a man who identified himself as Zam and "the founder of Amadnews," sitting in an armchair next to the flags of Iran and the IRCG.
In one clip, the man apologized, saying, "It is not right to trust governments, especially governments that show they do not have good relations with the Islamic republic," including the United States, Israel, Saudi Arabia, and Turkey.
The three arrests could complicate President Emmanuel Macron's efforts to ease tensions between Washington and Tehran.
Last week, France's Foreign Ministry warned French citizens against traveling to Iran, citing "regional tensions" and "arbitrary arrest and detention practices from the Iranian security services."
Iran has arrested dozens of dual nationals in recent years on alleged espionage charges.
Iranian authorities have not provided any evidence to back their claims.