Tunisian President Beji Caid Essebsi declared a nationwide state of emergency and a curfew in the capital after a bomb attack on a presidential guard bus killed at least 12 people on Tuesday.

A security source at the site said "most of the agents who were on the bus are dead" after the attack in Tunis, which has become a target of jihadist violence since 2011.

No group immediately claimed responsibility for the bombing, which a ministry official said also wounded 20 people when it went off on Mohamed V Avenue, just as this year's 26th Carthage Film Festival was in full swing.