Protests and a general strike swept Tunisia Friday after gunmen killed an opposition head with "the same gun" used to kill a colleague, as the authorities pointed to Al-Qaeda links.
Mohamed Brahmi was gunned down on Thursday with the same weapon used to kill another opposition politician, Chokri Belaid, six months earlier, Interior Minister Lotfi Ben Jeddou said.
Brahmi's wife Mbarka told AFP he will be buried on Saturday at El Jallez cemetery in southern Tunis next to Belaid, with the funeral procession starting from the family home at 0900 GMT.
Ben Jeddou said the main suspect in Brahmi's killing was a member of radical Sunni Muslim Salafist movement Ansar al-Sharia, that officials have previously linked to Al-Qaeda.
"The first elements of the investigation show the implication of Boubaker Hakim, a Salafist extremist," he said.
The 30-year-old Paris-born chief suspect was already wanted in Tunisia for kidnapping and arms trafficking, the minister said.
Public security chief Mustapha Taieb Ben Amor named 14 radical Islamist suspects -- including four behind bars -- implicated in the two political killings.
"The suspects are radical extremists, and some of them belong to Ansar al-Sharia," the main Salafist group in Tunisia, Ben Jeddou said.
Brahmi, 58, was gunned down outside his home in the Tunis suburb of Ariana by two gunmen on motorcycles.
He was an MP with the leftist and nationalist Popular Movement but quit the party he founded on July 7 saying it had been infiltrated by Islamists.
The General Union of Tunisian Labour (UGTT) called Friday's general strike in protest at "terrorism, violence and murders".
National airline Tunisair and some European carriers cancelled flights to Tunis on Friday.
Thousands of pro-government demonstrators also staged a solidarity rally in the capital amid allegations of government connivance in the killing.
The state prosecutor's office said an autopsy found that Brahmi had been cut down by a hail of 14 bullets.
Balkis Brahmi, 19, one of his five children, said he was killed by two men in black on a motorbike.
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"At around midday, we heard gunfire and my father crying with pain. We rushed out -- my brother, mother and I -- to find his body riddled with bullets at the wheel of his car parked in front of the house," she told AFP.
As news of the killing spread, angry protesters took to the streets in both Tunis and Sidi Bouzid, Brahmi's hometown.
His wife Mbarka said Saturday's funeral procession will travel 10 kilometres (six miles) from their home to the cemetery.
The interior ministry said it will deploy reinforcements to provide security as the UGTT called for a national funeral.
Tens of thousands of people attended Belaid's funeral in February when part of the procession turned into a protest against the ruling Islamist party Ennahda.
Ennahda was again in the firing line over Brahmi's death.
"Violence is being turned into a system. By whom? By people determined to seize power or to stay in power," Le Quotidien newspaper said, pointing the finger of blame at the government led by the moderate Ennahda.
Beji Caid Essebsi, head of the main opposition party Nidaa Tounes, said Ennahda was to blame because it had failed to identify Belaid's killers.
"There has not been any serious judicial action," he said.
Ennahda chief Rached Ghannouchi in a statement to AFP on Thursday said "those behind this crime want to lead the country towards civil war and to disrupt the democratic transition".
He called the killing a "catastrophe" for Tunisia, and the presidency said Friday was being marked as a day of national mourning.
Political tension has been rising in Tunisia, with the launch of its own version of the Tamarod (rebellion) movement in Egypt that led to the ouster of Islamist president Mohamed Morsi on July 3.
Brahmi's murder stoked the tension and one party, Al Moubadara, decided to withdraw its five MPs from parliament, a party official said.
The UN human rights office urged official restraint in the face of public anger.
"We urge the authorities in Tunisia to take great care not to inflame the situation further with excessive use of force and to respect the right of people to protest peacefully," spokesman Rupert Colville told reporters in Geneva.