Thousands of Tunisians took to the streets of the capital Tunis on Saturday to call for an end to an Islamist government they blame for the assassination of a leading secular politician 40 days earlier.

It was the biggest demonstration since Chokri Belaid was gunned down outside his house on February 6, igniting the worst unrest since the Jasmine Revolution that toppled strongman Zine al-Abidine Ben Ali in 2011 and started the Arab Spring.

In a bid to quell the protests, Prime Minister Hamadi Jebali resigned and was replaced by Ali Larayedh, a fellow member of the Islamist Ennahda party, who formed a new coalition government including independents in key ministries.

But protesters on Saturday blamed the ruling party for Belaid's murder and chanted "Ennahda go," "The people want a new revolution," and "The people want to bring down the regime."

No one has claimed responsibility for the killing, which Belaid's family blames on Ennahda. The party denies involvement and police say the killer was a radical Salafist Islamist.

Belaid, a left-wing lawyer, was shot at close range outside his Tunis home by an assassin who fled on a motorcycle.

His nine-party Popular Front bloc has only three seats in Tunisia's Constituent Assembly, which is acting as parliament and writing a new national charter, compared to some 120 for Ennahda and its partners. But Belaid spoke for many who fear religious radicals are stifling freedoms won in the Arab Spring.

The North African state's new Islamist-led government won a confidence vote on Wednesday although the death of an unemployed man who set himself on fire underscored popular discontent with high unemployment, inflation and corruption.

"They killed Chokri but they cannot kill the values of freedom defended by him," Belaid's widow Basma said in front of her husband's grave on Saturday.

Tunisia's transition has been more peaceful than those in Egypt and Libya, and has led to freedom of expression and political pluralism. But tensions run high between liberals and the Islamists who did not play a major role in the revolt but were elected to power.

The government is also pressing ahead with tax rises and subsidy cuts to reduce this year's projected budget deficit of 6 percent of gross domestic product, despite a storm of public criticism.

Lacking the huge oil and gas resources of neighbours Libya and Algeria, Tunisia's compact size, relatively skilled workforce and close ties with Europe have raised hopes it can set an example of economic progress for the region. Tourism is a major foreign currency earner.-Reuters