Tunisia is blaming al-Qaida-linked extremists for gunning down a leading opposition politician in broad daylight.
Interior Minister Loufti Ben Jeddou said Friday Mohamed Brahmi, with the secular Popular Front party, was killed with the same gun used to kill opposition leader Chokri Belaid in February. The interior minister also named the suspected gunman as Boubakr Hakim, a smuggler with jihadi sympathies.
Brahimi's assassination on Thursday has rocked Tunisia, sparking mass protests and a general strike.
Police used tear gas to try to disperse protesters who took to the streets of the capital, Tunis, overnight. But many said they would not be deterred.
"We are all against Ennahda. We are all exposed to bullets now. What if I am shot dead? But now, I am ready to die for the sake of my country."
Many of the protesters are blaming the country's ruling Ennahda party for the assassination, saying the moderate Islamist part had not done enough to cut off funding or support for more extremist groups.
The Popular Front's Brahimi was a vocal critic of Tunisia's Islamist-led government and was helping draw up a new constitution.
On Friday, spokesman Hamma Hammami said the Popular Front was ready to launch an alternative government.
"We (the opposition) agreed that this is the end of legitimacy of the National Constituent Assembly and institutions that emanate from it, as the presidency and government are over now."
Ennahda, which rules in a coalition with two secular parties, has condemned the killing.
The chairman of the Constituent Assembly declared Friday a day of mourning.
Thursday's killing comes as Tunisia was celebrating the 56th anniversary of becoming a republic after gaining independence from France.
Tunisia's 2011 uprising ousted autocratic President Zine al-Abidine Ben Ali and sparked a wave of similar protests across the Middle East and North Africa.