Yaacoub’s brother, Ali, called upon the demonstrators to join him for prayers “in the hope that he would be released soon.”
Former MP Hassan Yaacoub was arrested during his questioning over the kidnapping of the son of former Libyan leader Moammar Gaddafi.
Yaacoub's father was accompanying Imam Moussa al-Sadr and another man when they disappeared in Libya in 1978.