TUNIS, Tunisia -- Tens of thousands of Tunisians on Saturday called for the resignation of the Islamist-led government in one of the largest opposition protests to date.

The protest, organized by the National Salvation Front coalition of parties, marked the traditional 40-day mourning period since the assassination of opposition politician Mohammed Brahmi.

His killing in front of his family plunged the country into a political crisis and prompted dozens of opposition members of the assembly to withdraw from the body, paralyzing its work of writing the country's new constitution.

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Protest in Tunisia

People demonstrate against Tunisia's Islamist-led government, near the Constituent Assembly headquarters in Tunis, Tunisia, Saturday Sept. 7, 2013..(AP Photo/Hassene Didri)

They announced Friday they would begin a hunger strike until their demands were met.

Weeks of mediation by the main labour union between the moderate Islamist Ennahda Party and the opposition have not borne fruit.

"We are determined to continue the struggle to extract the country from the disastrous situation it finds itself in because of those in power," said Beji Caid Essebsi, leader of the right-of-centre Nida Tunis (Tunis Calls) party, one of the main opposition groups.

"After the blood, Ennahda has no legitimacy," chanted demonstrators who came from all over the country to answer the opposition call for the march.

When Tunisians overthrew their decades-old authoritarian government in January 2011, it sparked a wave of pro-democracy uprisings across the region, but the transition to democracy has been rocky since.

"Leave! The dictator understood, but you still don't understand," chanted the marchers, referring to how Tunisia's president fled for Saudi Arabia in the face of popular demonstrations.

The opposition is demanding the Islamist-led government resign immediately for what they say is its failure to ensure security or manage the economy.

Ennahda has countered by offering to dissolve the government after four weeks to ensure the constitution is completed and the body charged with organizing elections has been put in place. In August, Ennahda, which rules in a coalition with two secular parties, organized its own pro-government demonstration of comparable size.

The competing offers have been relayed over the past few weeks by a mediation team composed of the heads of the main labour union, known as the UGTT, the chamber of commerce, the bar association and the league for human rights. They also presented proposals of their own to resolve the crisis.

By the end of last week, however, Houcine Abassi of the UGTT indicated that the talks had broken down.

"We can't say that we've failed in our initiative, but we can't say that we've achieved our goals," a stern-faced Abassi said late Friday.

The opposition has held several protests since Brahmi's death, but Saturday appears to be one of the largest, and opposition leader Samir Taieb said more would come until Ennahda resigned.

"Today we are embarking on a new stage in the struggle to impose the solution proposed by the UGTT, the chamber of commerce, the lawyers and the league for human rights."

In the turbulent two and a half years since the fall of President Zine El Abidine Ben Ali, Tunisia has been wracked by a weak economy, militant attacks and social unrest.

But its fractious political parties have always managed to reach compromises on key issues. The latest standoff is the greatest crisis of the transition and a solution acceptable to both sides appears to still be distant.

With the overthrow of the elected president in Egypt by the military, there has been renewed focus on whether Tunisia's own transition will succeed.