Voters in Egypt have begun voting in a referendum on a new constitution.

The polls opened Saturday morning.

The lead-up to the voting has been marked by violence and protests.

Officials say they have deployed 120,000 soldiers to protect polling stations Saturday, when half the country's eligible voters cast their ballots. The rest of the country will vote December 22.

The proposed constitution has the support of President Mohamed Morsi's former party, the Muslim Brotherhood. Mr. Morsi resigned from the group when he became president earlier this year.

Members of the liberal, secular and Christian opposition say they fear it will erode civil liberties because it boosts the role of Islamic law and does not mention women's rights.

Clashes broke out Friday among stone-throwing demonstrators protesting the draft constitution near a mosque in Alexandria, prompting police to fire tear gas. Medical workers say 15 people were injured.

Also Friday in Cairo and other cities, thousands of flag-waving activists turned out for rival rallies. Such gatherings generally have been peaceful.

A largely Islamic committee approved the document last month after liberal and Christian members walked out, complaining they were being ignored.