Egyptian Islamists brandishing swords have clashed with opponents of a draft constitution in the city of Alexandria as tensions rose on the eve of a referendum on the disputed charter that has plunged the country into weeks of turmoil.

Egypt’s attorney general has referred an outspoken anti-Islamist former politician for investigation by police prosecutors over claims he called for the downfall of the regime, according to a statement.

A former strongman of ousted President Hosni Mubarak’s regime announced his presidential candidacy, shaking up an already heated race that is emerging as a contest between two long-time rivals – former regime officials and Islamists who have surged in influence.