Tunisia's president declared a day of mourning Friday after gunmen shot dead a leading opposition figure, plunging the country into fresh political turmoil, sparking protests and prompting calls for a general strike.
National airline Tunisair cancelled all flights on Friday, with more street protest expected amid allegations of government connivance in the killing.
MP Mohamed Brahmi, 58, of the leftist Popular Movement,was assassinated Thursday outside his home in Ariana, near Tunis, by gunmen on a motorbike, witnesses said.
"He was riddled with bullets in front of his wife and children," Mohsen Nabti, a fellow member of the small movement, said in a tearful account aired on Tunisian radio.
Human Rights Watch said that Brahmi's son, Adnen, had told its researchers he heard a first and a second gunshot, then several other shots as if from a machine gun.
He and his sister ran out of the house and as they reached their father's car they saw two men riding off on a motorbike, HRW said.
As news of the killing spread, protesters took to the streets Thursday in central Tunis and in Sidi Bouzid, the birthplace of the Arab Spring and Brahmi's home town.
Police in Tunis fired tear gas to disperse scores of demonstrators who tried to set up a tent for a sit-in calling for the fall of the regime.
The General Union of Tunisian Labour (UGTT) called a general strike for Friday in protest at "terrorism, violence and murders".
The Tunisian presidency, meanwhile, told AFP that Friday would be observed as a day of national mourning "following the assassination of lawmaker martyr Mohamed Brahmi".
The February 6 assassination of Chokri Belaid, another opposition figure, also outside his home, sparked a political crisis in Tunisia and charges the Ennahda party was involved.
Similar charges against Ennahda were quickly made over Brahmi's killing, which the moderate Islamist group has vehemently denied.
"I accuse Ennahda," the MP's sister Chhiba Brahmi told AFP at the family home in Sidi Bouzid. "It was them who killed him," she said, although she offered no evidence.
"Our family had the feeling that Mohamed would suffer the same fate as Chokri Belaid," whose family also blamed Ennahda, she added.
Ennahda chief Rached Ghannouchi rejected the charge in a statement to AFP. Brahmi's killing was "a catastrophe for Tunisia", he said.
"Those behind this crime want to lead the country towards civil war and to disrupt the democratic transition."
Political tension has been rising in Tunisia, with the launch of the country's own version of the Tamarod (rebellion) movement launched in Egypt that led to the ouster of Islamist president Mohamed Morsi on July 3.
According to the latest figures, dated July 14, the Tunisian group has collected 870,000 signatures on a petition demanding the national assembly be dissolved.
On Monday, Islamist Prime Minister Ali Larayedh criticised Tunisia's Tamarod movement, saying it represents a "danger to the democratic process" in Tunisia.
EU foreign policy chief Catherine Ashton condemned Brahmi's killing, adding her voice to calls by UN human rights chief Navi Pillay, Amnesty International and Human Rights Watch for an investigation into the incident.
The United States condemned the "cowardly" assassination.
-- 'Down with the Brothers' --
Brahmi was elected MP in October 2011 for Sidi Bouzid, birthplace of the revolution earlier that year that toppled Ben Ali.
On July 7, he resigned as general secretary of the Popular Movement, which he founded, saying it had been infiltrated by Islamists.
Following his killing, angry demonstrators took to the streets of Tunis to denounce the ruling Islamists.
Mohamed Maaroufi, a member of a youth committee that organised the protest, told AFP that they would stay in the streets until Ennahda had been forced from government.
In Sidi Bouzid, crowds, referring to the Muslim Brotherhood, chanted "Down with the Brothers, down with the people's torturers!"
Thousands also protested in nearby Menzel Bouzaine, where Ennahda party offices were set ablaze.
Prime Minister Ali Larayedh, himself an Islamist, told reporters: "I condemn in the strongest terms this odious crime which targets the whole of Tunisia and its security."
He also called for calm.
"This drama must not be exploited to sow trouble," he said. "Only minutes after news of the murder was announced, calls were made inciting Tunisians to kill each other."
President Moncef Marzouki said Brahmi's killing was a "second national catastrophe" after Belaid's murder.