Furious protesters on Wednesday erected barricades in central Tunis and hurled rocks at police who tried to disperse them with tear gas in new clashes after the assassination of a prominent opposition figure.
A national guard tank fired rounds of tear gas at the young protesters, who used bins, coffee tables, barbed wire and barriers to build the barricades on Habib Bourguiba Avenue, the epicentre of Tunisia's revolution two years ago.
Security reinforcements arrived after about 20 minutes of skirmishes, and police wearing helmets and armed with clubs charged some 150 protesters, who fled into the neighbouring streets.
Clouds of tear gas were visible in parts of the city centre, and by late afternoon there was a heavy security presence, with police bikes and lorries patrolling Habib Bourguiba Avenue, which was closed to traffic.
Chokri Belaid, a prominent figure in the coalition of leftist opposition parties and outspoken critic of the government, was gunned down as he left his home early on Wednesday.
The cold-blooded killing, which his family blamed on the ruling Islamist party Ennahda, sparked outrage, with thousands of people massing outside the interior ministry in Tunis, and in other cities.
In Sidi Bouzid, birthplace of the 2011 revolution that toppled ex-dictator Zine El Abidine Ben Ali, some 2,000 protesters took to the streets to denounce the murder.
The demonstrators were mostly peaceful, but about 200 people tried to storm the police headquarters and police used tear gas to keep them at bay.
Protesters also torched the Ennahda party office in Mezzouna, near Sidi Bouzid, ransacked another in the mining town of Gafsa, where they tore up Ennahda flags, and set fire to a party office in the northeastern town of Kef, witnesses said.
The murder of Belaid comes at a time of rising violence in Tunisia stoked by political and social discontent two years after the mass uprising that forced Ben Ali to flee and touched off the Arab Spring.