The assassination of Chokri Belaid, a widely-known Tunisian opposition figure and head of the Democratic Patriots Party, outside his home on Wednesday caused a series of angry reactions on official and public levels.
Tunisia was the first to oust its leader and hold free elections as uprisings spread around the region two years ago, achieving a relatively smooth transition to democracy.
However, the killing of Belaid added to an ongoing state of political unrest inside the North African state.
Ennahda, the Islamist party leading the ruling coalition, faced on Wednesday attacks on its offices along with protests that erupted in several towns.
More than 1,000 Tunisians protested outside the Interior Ministry against Belaid's killing, chanting for the fall of the Islamist-led government as security forces cordoned off the area.
Police forces responded by firing tear gas at protesters in the central town of Sidi Bouzid, birthplace of the 2011 revolution, as some 200 protesters attacked the local police station and threw rocks at police personnel.
In central Tunis a national guard tank fired rounds of tear gas at the young protesters, who used bins, coffee tables, barbed wire and barriers to build the barricades on Habib Bourguiba Avenue, the epicentre of Tunisia's revolution two years ago.
The army then intervened to calm the crowd in this marginalised town in central Tunisia, AFP reported.
"Shame, shame Shokri died; where is the government," protesters chanted.
"The government should fall."
"Shokri Belaid was killed today by four bullets to the head and chest ... doctors told us that he has died. This is a sad day for Tunisia," Ziad Lakhader, a leader of the Popular Front, told Reuters.
President Moncef Marzouki cut short a visit to France and cancelled a visit to Egypt scheduled for Thursday after the killing.
Prime Minister Hamadi Jebali said the identity of the killer remains unknown.
"The murder of Belaid is a political assassination and the assassination of the Tunisian revolution. By killing him they wanted to silence his voice," said Jebali.
Ennahda won 42 per cent of seats in the first post-Arab Spring elections in October 2011 and formed a government in coalition with two secular parties, President Moncef Marzouki's Congress for the Republic and Ettakatol.
Rached Ghannouchi, Ennahda's leader, denounced the murder of the secular opposition leader, claiming that the killers wanted a "bloodbath but they won't succeed."
"We can only condemn this cowardly act, which is aimed at [undermining] the revolution and the stability of Tunisia," he told AFP.
On the other hand, four Tunisian opposition groups, including Belaid's Popular Front, announced their withdrawal from the constitution-drafting national assembly and called for a general strike on the day of Belaid's funeral.
The family and supporters of Belaid blamed Ennahda for his assassination.
Nejib Chebbi, a leader of one of the groups, the Republican Party, said they also demanded the immediate resignation of Interior Minister Ali Larayedh, who is a member of Ennahda.
"We demand the departure of the interior minister and the dissolution of the League for the Protection of the Revolution as immediate first steps," Chebbi told AFP.
"The interior minister holds personal responsibility for the assassination of Chokri Belaid, because he knew he was threatened and he did nothing."
The League Chebbi referred to is a controversial group of pro-Ennahda militants that has been implicated in numerous attacks on secular opposition groups and trade unions since the revolution erupted two years ago.
The withdrawal decision was taken during a meeting that was attended by several movements such as Call of Tunisia, Al Massar and the Popular Front, an alliance of leftist and pan-Arab parties Belaid helped to form last year and which presents itself as an alternative to the Islamist-led ruling coalition.
Belaid, born in 1964, was a lawyer, opposition politician and former head of High Commission for the Realisation of Revolution Objectives, Political Reforms Democratic Transition.