Iran confirmed on Tuesday it had detained French-Iranian scholar Fariba Adelkhah.
A senior research fellow at Sciences Po university in Paris, Adelkhah, 60, was arrested in June by Iran’s Revolutionary Guards.
French President Emmanuel Macron said on Monday he was worried by the arrest.
Rights activists have accused Iran of arresting a number of dual nationals.
Adelkhah’s arrest comes at a time when France and other European powers are caught up in an international standoff over Tehran’s 2015 nuclear deal.