Tunisian opposition politician 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.
Mr Belaid was a prominent secular opponent of Tunisia’s government led by moderate Islamist Ennahda party.
According to the AFP news agency, Ennahda offices have been attacked and protests have broken out in several Tunisian towns.
Crowds have gathered outside the interior ministry chanting they want a “second revolution”, the BBC’s Sihem Hassaini in Tunis says.
Prime Minister Hamadi Jebali said his murder was an “act of terrorism” and a blow to the country’s Arab Spring revolution, which took place in January 2011.
“This is a criminal act, an act of terrorism not only against Belaid but against the whole of Tunisia,” Mr Jebali told Tunisia’s privately owned FM Radio Mosaique, promising to pursue all efforts to “immediately” arrest the murderer.
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.
President Moncef Marzouki has cancelled his trip to Cairo, where he was to attend the summit of the Organisation of Islamic Co-operation, and is to return home from a visit to Strasbourg by Wednesday afternoon.
‘Death threats’
“My brother was assassinated. I am desperate and depressed,” Mr Belaid’s brother Abdelmajid Belaid told AFP.
It is not known who is responsible for the attack on the politician.
Mr Belaid was the co-ordinator of the left-leaning Democratic Patriots party, part of a group of opposition parties which has been challenging the government since it came to power following the country’s first post-Arab Spring election in October 2011.
On Saturday, he accused “mercenaries” hired by the Ennahda party of carrying out an attack on a Democratic Patriots meeting.
The Paris-based France 24 TV station has reported that Mr Belaid reportedly received recent death threats.
It said that he died in hospital after being shot by “three men in a black vehicle” who fired two bullets into his chest and neck.
Correspondents say that although Mr Belaid’s party did not have a large share of the election vote, it spearheaded popular concern over the rising level of political violence in Tunisia.
BBC