Hundreds of students supporting Egypt's ousted president are battling security forces at a main Cairo university — two days before a planned vote on a draft constitution.

The clashes Sunday came as Egypt's Interim President Adly Mansour urged voters to head to the polls to cast ballots Tuesday and Wednesday. Mansour said that the draft charter used "moderate" Islam as a base for legislation. He also asked voters "to lead the ship of the nation to the shores of safety."

Egypt's more than 52 million voters will decide whether to support amendments to the constitution initially drafted under toppled Islamist President Mohammed Morsi. The military overthrew Morsi in a popularly backed coup in July.

The military-backed interim government sees the vote as a milestone in legitimizing Morsi's removal.