Tunisian authorities said on Wednesday a suicide bomber wearing a vest packed with plastic explosive blew up a presidential guard bus a day earlier, killing at least 12 troops in an attack claimed by Islamic State militants.
Tuesday's explosion on a main boulevard in the capital drove home the vulnerability of Tunisia to Islamist militancy, following assaults on a seaside tourist hotel in June and the Bardo Museum in Tunis in March also claimed by Islamic State.
One of the Arab world's most secular nations, Tunisia has increasingly become a target for militants after being hailed as a beacon of democratic change in the region since its 2011 uprising ousted autocrat Zine Abidine Ben Ali.