Iranian authorities prevented a dissident scholar who was scheduled to give a speech at the Massachusetts Institute of Technology from leaving Tehran on Sunday, the Iranian Student News Agency reported, according to an article published by the Khaleej Times, a newspaper in Dubai, United Arab Emirates. The scholar, Hashem Aghajari, told the news agency that he “had all relevant documents and even the exit permit,” but was barred from boarding his flight.

Mr. Aghajari, a history professor at Tarbiat Modarres University, is a well-known critic of Iran’s Islamic system and has been imprisoned and twice was under death sentence for his views. He served almost two years in prison before he was released, in 2004.