Police fired tear gas to separate scores of opponents of the constitution and thousands of Islamists who clashed in the rain near a mosque in Alexandria yesterday.
The Islamists had gathered in support of an Islamic vision of Egypt's future a day before a second round of voting in a referendum on the basic law. Opposition supporters had also turned out as worshippers assembled for Friday prayers.
Mursi and his Islamist allies back the draft constitution as a vital step in Egypt's transition to democracy almost two years after the fall of Hosni Mubarak.
The opposition says the draft, drawn up by an Islamist-dominated assembly, is a recipe for deeper division and violence.
The run-up to the final round of voting on the new constitution on Saturday has been marked by often violent protests that have cost at least eight lives.