Several thousand people demonstrated on Saturday on the 40th day of mourning after the murder of opposition leader Chokri Belaid, a critic of the ruling Islamists whose death plunged Tunisia into turmoil.
People began gathering in the cemetery in southern Tunis where Belaid is buried. He was gunned down outside his home on February 6 in a killing blamed by the authorities on radical Islamists, denying any involvement.
Several arrests in the case have been made, but the suspected killer remains at large.
The crowd, who included Belaid's widow Basma and opposition political leaders, then headed for Habib Bourguiba Avenue in the city centre, chanting slogans against the ruling Ennahda party and its chief Rached Ghannouchi.
"The people are convinced Ghannouchi killed Belaid," "Killer Ghannouchi" and "Vengeance, vengeance!" they chanted amid a heavy security presence, as well as: "Clashes on the street until the fall of the government."
Several demonstrators also held placards demanding to know "Who killed Chokri Belaid?"
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Maya Jribi, a leader of the secular opposition Republican party, told AFP she was there to pay homage to Belaid.
"But we are also here to demand that the government reveal who killed him, who was behind this murder, and why he was killed." she added.
The leftist opposition leader's murder plunged the country further into political crisis two years after Tunisia toppled dictator Zine El Abidine Ben Ali in a revolution that touched off the Arab Spring.
It resulted in the resignation of Islamist premier Hamadi Jebali after he failed to persuade Ennahda to agree to a government of technocrats to lead the country until the adoption of a new constitution and elections.
A new government headed by former interior minister Ali Larayedh, also of Ennahda, was finally sworn in on Thursday, leading an uneasy coalition between the Islamists and two secular parties, in addition to independents.
Larayedh has pledged to resolve the political crisis this year by adopting a new constitution, organising elections, creating conditions for a revival of the economy and restoring security.