Tunisian unions have called a general strike after a leading opposition figure was assassinated, prompting thousands to take to the streets to protest and sparking international condemnation.
Shops an banks were closed and the country's national airline Tunisair cancelled all flights on Friday, as the General Union of Tunisian Labour (UGTT) called for the nationwide strike in protest against "terrorism, violence and murders", after gunmen shot MP Mohamed Brahmi outside his home.
The country is observing a day of mourning on Friday following the assassination.
Al Jazeera's Youssef Gaigi, reporting from Tunis, said that people were shocked by the assassination, which came during the assassination of the celebration of the day when the Tunisian republic was announced and constituted.
"There are already people protesting right now in front of the general union in Tunis and going out to the main street," Gaiga said.
Riot police fired tear gas at protesters in the Tunisian capital Tunis on Thursday, as thousands massed at the interior ministry over the shooting of Brahmi earlier in the day and tried to set up a tent for a sit-in calling for the fall of the government.
The ruling Ennahda party, a moderate Islamist group, denied accusations from the father of five's family that it was involved the murder member of the People Movement Party, which is part of the same coalition as Chokri Belaid, another prominent politician who was assassinated in February.
The UGTT last called a two-hour general strike on January 14, 2011, the day former Tunisian leader Zine El Abidine Ben Ali fell.
Brahmi, 58, was shot dead in front of his house in Ariana, near Tunis, on Thursday morning, state television and the official TAP news agency reported.
"He was riddled with bullets in front of his wife and children," said Mohsen Nabti, a fellow member of the small leftist movement, in a tearful account on Tunisian radio.
Friday will be a day of mourning in Tunisia, the chairman of the Constituent Assembly said.
Navi Pillay, UN human rights chief, condemned the killing of Brahmi and demanded an investigation into his slaying.
"I am shocked and deeply saddened by the news of Mr. Brahmi's assassination. I call upon the authorities to immediately launch a prompt and transparent investigation to ensure that the people who carried out this crime are held accountable," Pillay said in a statement.
The slain politician's widow, Mbarka Brahmi, told the Reuters news agency "this criminal gang has killed the free voice of Brahmi," without specifying who she thought was behind the shooting.
Brahmi's sister, Souhiba, meanwhile, accused the main Islamist Ennahda party of being behind the killing.
"Ennahda killed my brother," she said. Ennahda has condemned the murder.
In the southern town of Sidi Bouzid, the cradle of the Tunisian revolution, protesters set fire to two local Ennahda party offices, witnesses told Reuters.
"Thousands have taken to the streets. People have blocked roads and set tyres alight," said Mehdi Horchani, a resident of Sidi Bouzid. "People are very angry."
On Wednesday, Noureddin B'Hiri, senior adviser to the prime minister, said that six people believed to have orchestrated the killing of Belaid more than five months ago had been identified.
"We have identified the sponsors and the authors of the assassination of Chokri Belaid," B'Hiri said after a cabinet meeting.
B'Hiri had said that the details would be revealed "soon" by Interior Minister Lotfi Ben Jeddou, without saying when.
Belaid was shot dead outside his home on February 6, in an attack that shocked Tunisians and led to a political crisis that brought down the government of Prime Minister Hamadi Jebali.
The interior ministry blamed the killing of Belaid, who was an outspoken critic of Jebali's ruling Ennahda party, on a cell of "radical Islamists".
In April, the government released the photos and names of five suspects and appealed for help in arresting them.
Since the revolution that toppled Ben Ali in January 2011, "hardline Islamists" have been blamed for numerous acts of violence, notably an attack on the US embassy last September that left four assailants dead and the killing of Belaid.