Police in Tunis have used tear gas to try to disperse hundreds of Islamists who were attacking them with stones and knives.
One group of protesters was said to be angry over a ban on women who wear the niqab from enrolling in university.
Another group attacked a TV station that had shown a film which they claimed was blasphemous.
Police arrested dozens of mainly young men after the clashes, which were the biggest over religion in the Tunisian capital for several years.
Tension is mounting in Tunisia before an election later this month, the first since a revolution toppled the country’s autocratic leader.
The poll is for an assembly to draft a new constitution. The Islamist Ennahda party is expected to win the biggest share of the vote, alarming secularists who have traditionally dominated the ruling elite.