Tunisian police fired tear gas in front of parliament to disperse secular protesters demanding the dissolution of the assembly and Islamists defending the legitimacy of their rule.
Police began firing after the arrival of thousands of opposition protesters.
The protesters had been attending the funeral of the assassinated secular politician Mohamed Brahmi, a Reuters reporter said.
Protesters threw stones back at police and there were several injuries.
Among those wounded was an opposition politician from the same party as Mr Brahmi.
Secular opposition parties are demanding the dissolution of the Islamist-led government and parliament, known as the constituent assembly, which has been tasked with drafting a new constitution.
People in the crowd shouted: "The people want to topple the regime!" and "With our blood and with our souls we will sacrifice ourselves for the martyr!"
"Ghannouchi, assassin, criminal," others chanted, referring to Rached Ghannouchi, leader of the ruling Islamist Ennahda party that Brahmi's family blames for the killing.
Mr Ghannouchi denounced Thursday's assassination as an attack on the country's tumultuous process of transition from autocratic regime to democratic state.
In a counter-demonstration, hundreds of Islamists flocked in front of the parliament, chanting slogans condemning what they called an attempted coup against democracy.
The Interior Ministry issued a statement calling for calm.
