Violence broke out in the central city of Kairouan and in the capital Tunis after Tunisian police clashed with hundreds of hardline Islamists.
One protester was killed and 15 policemen injured in the street battles.
The government last week said it had barred the Salafist movement Ansar al-Sharia from holding its annual congress in Kairouan, saying it posed a threat to public security, reports the BBC.
The group urged its supporters instead to gather for the meeting in the Tunis suburb of Ettadhamen, using its Facebook page.
Some 500 supporters were reported to have descended on Ettadhamen on Sunday, hurling stones at police who responded by firing tear gas and shooting into the air.
The government on Friday said it was banning Ansar al-Sharia from gathering in Kairouan because it had "shown disdain for state institutions, incited violence against them and poses a threat to public security".
The governing Ennahda party governs in coalition with two non-religious parties and has promised not to ban alcohol or impose the veil.
But Salafists want stricter Islamic laws imposed in Tunisia, and are demanding the introduction of Sharia.
