Thousands of Tunisians took to the streets of Bardo, near the capital Tunis, late Saturday, calling for the government led by the moderate Islamist Ennahda party to step down.
They were marking the end of a 40-day period of mourning after the assassination of opposition leader Mohamed Brahmi, shot dead outside his home on July 25.
Protesters gathered at Bab Saadoun, on the outskirts of Tunis, before marching to Bardo square, the scene of regular protests after the killing of Brahmi.
Demonstrators carrying portraits of Brahmi chanted slogans paying tribute to him and denouncing the government.
The authorities have blamed Brahmi's killing, and the murder in February of another opposition figure, Chokri Belaid, on Salafist militants.
But many opposition supporters blame the government for having failed to crack down on Islamist extremists in the wake of Belaid's killing.
Some members of Brahmi's family have accused Ennahda itself of being behind his assassination, a charge the party has repeatedly denied.
Members of Brahmi's family and a number of friends of Belaid marched at the head of the rally.
Brahmi's widow had made it clear that government representatives would not be welcome at any of the ceremonies in memory of her husband. She too called for the government to go.
The National Salvation Front, an umbrella group of opposition parties that has led the campaign against the government since Brahmi's murder, promised to keep up the pressure on the government.
But Ennahda has so far resisted the Front's calls for it to step aside in favour of a non-partisan cabinet. Instead, it has offered to broaden the existing ruling coalition and to hold elections in December.
It wants the National Constituent Assembly to be allowed to finish its work drawing up a new constitution for the country.
It would replace the one that existed during the rule of long-time president Zine el Abidine Ben Ali, who was ousted in the 2011 "Arab Spring" revolution.