Tunisia's national airline Tunisair cancelled all flights on Friday.

MP Mohamed Brahmi, a father of five, was shot by unknown gunmen outside his home on Thursday in the second such political assassination this year.

The ruling Ennahda party denied accusations from his family that it was involved.

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 government.

The General Union of Tunisian Labour (UGTT) called Friday's general strike across the country in protest at "terrorism, violence and murders".

It last called a two-hour general strike on January 14, 2011, the day former Tunisian dictator Zine El Abidine Ben Ali fell.

The February 6 assassination of Chokri Belaid, another opposition figure, also outside his home, sparked a political crisis in Tunisia and charges of government connivance.

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.