The trial of 24 people accused of links to the 2013 assassination of prominent Tunisian opposition figure Chokri Belaid opened briefly Tuesday but was postponed until October 30, a prosecution spokesman said.
"At the request of the plaintiff and the defence of the accused, the tribunal has decided to postpone the trial to October 30," Sofiene Sliti told AFP.
The court rejected demands for some of the suspects to be released, Sliti added.
Almost 200 lawyers, as well as police in plainclothes and journalists, attended the hearing, as dozens of people protested outside, chanting: "Tunisia is free! Terrorism out!"
To avoid the crowds, the session was held in a hall on the first floor of the Palace of Justice in Tunis, rather than in a main courtroom.
Lawyer Slah Hajri told the judge that the hall was not the appropriate setting for the "historic trial that the Tunisians are waiting for".
"We will find out today whether or not justice will be served. There will be signs on whether there is a will to serve justice," Belaid's widow Basma Khalfaoui earlier told AFP.
Belaid, who was gunned down outside his home on February 6, 2013, was a staunch leftwing critic of the then ruling Ennahda party, a moderate Islamist movement.
The suspects face several charges, including "incitement to commit terrorist crimes" and "membership of groups linked to a terrorist organisation", one of their lawyers said.
They are also suspected of providing information and funds to people known for "terrorist activity", as well as weapons and explosives to others with links to "terrorists".
Only four of the suspects could be seen in the hall where the opening hearing was held. The prosecution said all but one of the suspects are in custody.
The rest of the accused were also brought to the courthouse but refused to stand before the judge, their lawyers said.
"For a week, the accused have been suffering a wave of aggression" at Borj Erroumi and Mornaguia prisons, "where they are even prohibited from praying", lawyer Sarra Harath told the judge.
"So long as their rights are not respected, they will refuse to stand before the court," she added.
Belaid's murder triggered deadly protests and a political crisis that brought down Islamist prime minister Hamadi Jebali.
Five months later, Tunisia plunged into further crisis with the murder of another opposition figure, Mohamed Brahmi.
Jihadists claimed both killings and the authorities announced in February 2014 that Belaid's assassin had been killed in a police raid on "terrorist" suspects.
But Belaid's family has repeatedly demanded the full truth behind the murder.
The trial opened four days after 38 people, mostly British holidaymakers, were killed as a jihadist gunman went on a shooting rampage on a Tunisian beach, in the second attack in three months on tourists in Tunisia claimed by the Islamic State group.