An Iranian lawyer representing two French researchers in custody in Tehran says that prosecutors have given no evidence to support the spying and security charges against them.
The semiofficial ISNA news agency quoted lawyer Saeid Dehghan on October 28 as saying that Roland Marchal, a researcher at Sciences Po in Paris, was detained on security charges in June while visiting Iran to see Fariba Adelkhah, an academic at the same university.
Adelkhak was also arrested on espionage charges.
The two are believed to have been in a romantic relationship.
"Up until this moment, the reasons for my clients' charges, which according to Article 32 of the constitution must be given alongside the charges, have not been mentioned," Dehghan said.
"It seems that Mr. Marchal has been arrested because of his friendship with Ms. Adelkhah," he added.
The lawyer said the two cases were still at the level of prosecutors and had not yet been sent to court.
The French government has called for their immediate release and condemned what it described as "an unacceptable situation."
Iran does not recognize dual nationality for its citizens.
Iran has also detained at least two other dual nationals -- Iranian-British anthropologist Kameel Ahmady and Iranian-British national Nazanin Zaghari-Ratcliffe.
Both have been accused of spying and of connections to foreign intelligence agencies.