Iranian authorities on Tuesday confirmed the detention of a French-Iranian academic.
Academic Fariba Adelkhah "was detained recently," judiciary spokesman Gholamhossein Esmaili told a press conference in Tehran.
He, however, said "due to the nature of the case, this is not the proper time to give any information about it".
The spokesman said more details will be announced "as the case progresses".
On Monday, the French Foreign Ministry demanded immediate consular access to Adelkhah.
"France calls on the Iranian authorities to shed full light on Mrs Adelkhah’s situation and repeats its demands, particularly with regard to an immediate authorization for consular access. No satisfactory response has been received until now,” the ministry said in a statement.
Iranian opposition said Adelkhah, who is best known for her book Being Modern in Iran, about changes in Iran after the 1979 Islamic revolution, has disappeared in Tehran since last month.
From time to time, the Iranian authorities arrest Iranian dual nationals on security-related charges.