Tunisian opposition leader Mohamed Brahmi has been assassinated outside his home in Tunis, officials say.
Mohamed Brahmi, 58, led the nationalist Movement of the People party.
It is the second time an opposition party leader has been killed this year.
In February, prominent secular politician Chokri Belaid was also shot outside his house in Tunis. His murder sparked protests and forced PM Hamadi Jebali to resign.
An uprising in Tunisia in late 2010 kick-started a series of revolutions that spread through the Middle East and became known as the Arab Spring.
Gunmen on a motorbike shot Mohamed Brahmi in his car in front of his wife and daughter on Thursday morning, Movement of the People party officials said.
Local media said the assailants fired 11 bullets at the politician. It is not known yet who was behind the attack.
Mohamed Brahmi’s wife, Mbarka, said a “criminal gang has killed the free voice of Brahmi”.
Mbarka Brahmi and her daughter Belkis were joined by angry Tunisians outside the hospital in Ariana where the politician died.
Mohamed Brahmi has been assassinated outside his home in Tunis
Large crowds also gathered outside the Ministry of Interior in Tunis in protest at the killing.
There are also reports of demonstrators converging in the city of Sidi Bouzid, Mohamed Brahmi’s hometown and the birthplace of the Arab Spring.
“People have blocked roads and set tyres alight,” a local resident told the Reuters news agency.
The governing Islamist Ennahda party expressed “sadness and shock” at the assassination, which it described as a “cowardly and despicable crime”.
The killing came as Tunisia celebrated the 56th anniversary of becoming a republic after gaining independence from France.
French President Francois Hollande condemned Mohamed Brahmi’s murder and called on Tunisians to unite behind the democratic transition.
Mohamed Brahmi founded the Movement of the People party after the 2011 revolution.
He was also a member of the National Constituent Assembly, which is drafting a new constitution.
The assembly announced Friday would be a day of mourning.
Mohamed Brahmi was not as big a political figure as Chokri Belaid, but he too was a leftist critical of Ennahda.
Ennahda came to power following the overthrow of long-term ruler Zine al-Abidine Ben Ali in January 2011.
The party has faced growing popular unrest over a faltering economy and a rising extremist Islamist movement.
After Chokri Belaid’s assassination in February, many Tunisians accused Ennahda of not doing enough to stamp out a rise in Islamist violence, with some critics saying the party was actively fomenting it, correspondents say.
The party denied the accusations.
Thousands of people have attended the funeral of Tunisian opposition leader Chokri Belaid, who was killed on Wednesday by a gunman who fled on a motorcycle.
There were minor clashes as Chokri Belaid’s coffin was carried through Tunis, but the event was largely peaceful.
Sporadic protests and clashes have been reported all around Tunisia, and many workers are observing a general strike.
Unions say the Islamist-led government is to blame for the killing, an accusation it denies.
PM Hamadi Jebali has tried to defuse tension by calling for a non-partisan technocratic government. However, his governing Ennahda party has refused to accept this.
Some 3,000 people initially gathered outside the building in the Djebel Jelloud suburb of Tunis where Chokri Belaid’s flower-covered coffin lay.
Crowds chanted slogans accusing the government of murdering Chokri Belaid, 48.
“With our blood and our souls we will sacrifice ourselves for the martyr,” the mourners shouted.
Thousands more people then joined the coffin as it was taken on a funeral procession toward the nearby cemetery of el-Jellaz.
Many more people are expected to take to the streets of the capital after Friday prayers and ahead of the burial in the afternoon.
Hundreds of riot police have been deployed in Habib Bourguiba Avenue, the scene of earlier violence.
Police fired tear gas to break up youths attacking cars close to el-Jellaz cemetery, and also at protesters near the interior ministry.
Elsewhere in Tunis, many shops are shut and most public transport is not running.
This is the first general strike in 35 years.
A number of flights to and from Tunis-Carthage airport have been cancelled.
Thousands of people have attended the funeral of Tunisian opposition leader Chokri Belaid, who was killed on Wednesday by a gunman who fled on a motorcycle
Tunisian state television said universities had been ordered to suspend lectures on Saturday and Sunday, while France said it would close its schools in Tunis.
In the city of Sidi Bouzid, some 10,000 people also gathered to mourn Chokri Belaid.
In the central town of Gafsa, tear gas was fired amid clashes between protesters and security forces, witnesses and local media said.
Tension had been simmering for many months between liberal, secular Tunisians and the Islamist-led government.
Critics say that Ennahda has allowed ultra-conservative Muslim groups to impose their will on a bastion of Arab secularism.
Chokri Belaid was the victim of the first political assassination in Tunisia since the Arab Spring uprising in 2011.
Thousands of people later rallied outside the interior ministry in Tunis, many chanting slogans urging the government to stand down and calling for a new revolution.
In the centre of the capital, a police officer was killed during clashes between police and opposition supporters.
Also on Thursday, demonstrators observing a symbolic funeral for Chokri Belaid outside the governor’s office in Gafsa clashed with police.
One policeman was said to be in a coma on Friday after being dragged from his car and beaten in the town, the AFP news agency reported.
In Sfax, crowds ransacked a number of shops on Thursday.
Tunisian media reported that more than a dozen Ennahda offices across the country were attacked overnight.
Earlier, four opposition groups – including Chokri Belaid’s Popular Front – announced that they were pulling out of the country’s constituent assembly in protest.
Chokri Belaid was a respected human rights lawyer and left-wing secular opponent of the government which took power after the overthrow of long-serving ruler Zine el-Abidine Ben Ali.
Current President Moncef Marzouki said the assassination should not affect Tunisia’s revolution. He cut short a visit to France and cancelled a trip to Egypt to return home to deal with the crisis.
Tunisian opposition leader Chokri Belaid has been shot dead outside his home in the capital, Tunis, his brother and officials say.
They say that Chokri Belaid was shot in the neck and head on his way to work.
Chokri Belaid was the co-ordinator of the left-leaning Democratic Patriots party.
Tunisia is gripped by a political crisis as talks on a long-awaited cabinet reshuffle to include a wider range of parties in a coalition led by the Ennahda party have broken down.
“My brother was assassinated. I am desperate and depressed,” Chokri Belaid’s brother Abdelmajid Belaid told the AFP news agency.
It is not known who is responsible for the attack on the politician.
On Saturday Chokri Belaid accused “mercenaries” hired by the Ennahda party of carrying out an attack on a Democratic Patriots meeting.
Tunisian opposition leader Chokri Belaid has been shot dead outside his home in the capital, Tunis