Tens of thousands of Tunisians crowded the streets of downtown Tunis on Tuesday to demand the government's ouster, in the largest opposition protest in the capital since the country's political crisis began two weeks ago.
The secular opposition is trying to topple the Islamist-led government and dissolve a transitional Constituent Assembly that is only weeks away from finishing a draft constitution and new election law.
Tunisia is facing the worst political turmoil since autocratic ruler Zine el-Abidine Ben Ali was toppled, a crisis that has been compounded by growing instability as Islamist militants step up their attacks.
The protest on Tuesday marked the six-month anniversary of the assassination of leftist politician Chokri Belaid, one of two opposition figures to be shot dead in recent months. Fellow leftist Mohamed Brahmi was gunned down on July 25.
"The people want the fall of the regime," crowds crammed into Bardo square shouted, using the same slogan they popularized when Tunisians ousted Ben Ali in 2011 and sparked a wave of uprisings across the Arab world.
Organizers of pro-government demonstrations said more than 150,000 rallied a few days earlier in defense of the ruling Ennahda party, the largest crowds to assemble since Ben Ali's ouster.
Mongy Rahoui, a leader in the opposition's Popular Front, said of Tuesday's demonstrations: "These legions of crowds are a response to (Ennahda leader Rachid) Ghannouchi and we say to him we are ready for any referendum ... we are the ones with legitimacy on the streets. Your legitimacy is counterfeit."
A Reuters witness at the opposition protest on Tuesday said numbers were close, but not as high as the Ennahda rally.
On Monday, Ghannouchi told Reuters that changing the prime minister and dissolving the Constituent Assembly were "red lines" he would refuse to cross, but said he was willing to take the opposition's challenge against the government to a popular referendum and hold talks with his rivals.
In another surprise move that could risk worsening the political crisis, the head of the Constituent Assembly on Tuesday suspended its work, just as the protests started. He said the Assembly would not reconvene until the government and opposition began a dialogue.
"I bear responsibility as president of the Constituent Assembly for suspending the work of the council until a dialogue is started," Mustafa Ben Jaafar said in a televised speech.
"This is in the service of Tunisia in order to guarantee its transition to democracy."
Meanwhile, security forces are facing a surge in violence blamed on militants.
Earlier on Tuesday evening, police shot dead an Islamist militant in a suburb of Tunis, an interior ministry official said.
Attacks spiralled after the Brahmi assassination in July. Militants killed eight soldiers on July 29 near the Algerian border in one of the deadliest attacks on Tunisian forces in decades.
Since then, there have been near-daily reports of foiled bomb attempts or police raids against militants across the country.