Tens of thousands of Tunisians have taken to the streets to renew their demands that the Islamist-led government step down and end a political deadlock threatening the North African country's fledgling democracy.

Saturday’s rally was the largest protest since Tunisia's crisis erupted over the killing of an opposition leader in July, increasing pressure on the ruling Ennahda party to make way for a caretaker government before proposed elections.

Waving red and white national flags and pictures of slain opposition leader Mohamed Brahmi, protesters packed streets around a building where a national assembly had been drafting a new constitution until its work was suspended due to unrest.

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.

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.

Divisions between Tunisia's Islamists and their secular opponents have widened since the uprising that ousted President Zine al-Abidine Ben Ali, a revolt that triggered unrest across the Arab world and toppled rulers in Egypt, Libya and Yemen.

Tunisia's transition since that revolt has been relatively peaceful, with the moderate Islamist Ennahda party sharing power with smaller secular parties.

But tensions have increased in the nation of 11 million since Brahmi was killed in July, just months after another secular opposition figure was murdered by gunmen, who authorities say were tied to radical Islamists.

Protester Jouini Ezzedine held his hands in the air as he joined in choruses of anti-government chants, wearing plastic gloves dyed red to resemble what he said were the blood stained hands of the Tunisian regime.

"This is not a legitimate government, this is assassinations, explosions and terrorism," he said.

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.

Drawn-out wrangling over political control, elections and a new constitution now threatens transition and economic growth in a country once seen as the most promising example for the region's nascent democracies following the "Arab Spring".

The head of the constituent assembly about to finish drafting the new constitution halted its work after the opposition leader's assassination in July, throwing the country's transition off track.

Source: Agencies