Prominent Iranian lecturer Mehdi Zakerian has been prevented from leaving the Iran to take part in a conference in Italy.
Zakerian's lawyer, Mohammad Sharif, told Radio Farda that legal issues and transitional justice in the Palestinian territories were to be discussed at the conference.
Zakerian, a board member of Iran's Center for Scientific Research and Middle East Strategic Studies, was detained in 2008 on espionage charges.
His passport and other personal belongings, including his computer and research papers, were confiscated at the airport.
Sharif told Radio Farda that authorities did not return Zakerian's passport and he was unable to attend the conference.
He said the 2008 charges against Zakerian were based on his contacts with foreign diplomats, which he maintained because of his work and research activities.
No verdict on his case has been issued but a court hearing was held in February.
Zakerian has published several books and papers on international developments and human rights issues.