Tunisia imposed a curfew on Tuesday night on eight regions including the capital after some of the worst violence since the overthrow last year of President Ben Ali.
Earlier, youths had rampaged through the streets of Tunis, hurling rocks and petrol bombs at police stations and a court house. More than 160 people are said to have been detained
The unrest poses one of the biggest threats yet to Tunisia’s democratic transition.
The al-Qaeda leader Ayman al Zawahri has recently urged Tunisians to turn against the government.
Some analysts say his statement may have inspired the violence while the government blames Salafi Islamists.
The clashes follow Monday’s break-in at an art exhibition in which ultra conservative Islamists destroyed several works which they described as blasphemous and an insult to Islam.