Thousands of opposition activists have protested in central Tunis, demanding the resignation of Tunisia's Islamist-led government, before a national dialogue aimed at ending months of political deadlock.
The protesters gathered on central Habib Bourguiba Avenue in the capital, waving Tunisian flags and shouting slogans such as: "The people want the fall of the regime", "Get out" and "Government of traitors, resign!"
Wednesday's demonstration took place amid a heavy security presence, with armoured vehicles and anti-riot police deployed along the Tunis boulevard, which was the epicentre of the January 2011 revolution that ousted former President Zine El Abidine Ben Ali.
A rival rally planned by the League for the Protection of the Revolution, a controversial pro-government armed group, failed to materialise.
It is not a coincidence that they decided to attack the National Guard today. Every time we reach a consensus terrorism rises again
Wednesday's demonstration came just hours before the start of a planned national dialogue between the ruling party Ennahda and the opposition, which has now been delayed until Friday.
Mediators hope the talks will bring an end to the political paralysis gripping the country since the July killing of opposition MP Mohamed Brahmi and mark a crucial step in the country's democratic transition.
"We hope that Larayedh will have enough courage to announce the resignation of his government within three weeks to save the country," Hamma Hammami, a leader of the opposition Popular Front party, told AFP news agency.
The Tunisian Prime Minister Ali Larayedh on Wednesday confirmed Ennahda was ready to resign, but insisted on the completion of the country's new constitution, the establishment of an electoral commission and a clear election date before handing over power.
Meanwhile, seven Tunisian police were killed and one injured in clashes with gunmen, as the country waited for the government's expected resignation and the launch of talks on ending months of political deadlock.
Fighting erupted in the central Sidi Bouzid region, when members of the National Guard raided a house where the gunmen were holed up, a police source told AFP news agency.
President Moncef Marzouki announced three days of national mourning.
"It is not a coincidence that they decided to attack the National Guard today. Every time we reach a consensus terrorism rises again," he said.
According to a political roadmap drawn up by mediators, the national dialogue will lead within three weeks to the formation of a new caretaker cabinet of technocrats.
Negotiators will also have one month to adopt a new constitution, electoral laws and a timetable for fresh elections, key milestones in the democratic transition which has effectively been blocked by wrangling between the Islamists, their coalition allies and the opposition.
A coalition of secular opposition parties are demanding the immediate departure of the government, which it accuses of clinging to power.
A senior member of Ennahda charged on Tuesday that the opposition was preparing to "destroy" the negotiations between the two sides by staging anti-government protests.
About 60 opposition MPs who have been boycotting parliament since the political crisis erupted, also said they had received assurances that the national dialogue would begin with the government announcing its resignation.
The Islamist party was heavily repressed under the Ben Ali regime.
Since triumphing in the parliamentary elections in October 2011, they have been weakened by accusations that they have failed to fix Tunisia's lacklustre economy and prevent attacks by armed groups.
After three months of political uncertainty, unkept promises and a false start to the national dialogue on October 5, the Tunisian press has grown increasingly critical of the ruling elite and sceptical of efforts to end the crisis.