CAIRO (AP) -- Hundreds of students supporting Egypt's ousted president battled security forces Sunday at three Cairo universities, two days before a referendum that officials say will be protected by a massive deployment of soldiers and police.
The clashes came as Egypt's Interim President Adly Mansour urged voters to head to the polls to cast ballots Tuesday and Wednesday on the draft constitution. 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 on July 3 and two panels dominated by secular-leaning politicians and legal experts later rewrote the document.
A large turnout and a strong "yes" vote would give legitimacy and a boost to a military-backed plan for presidential and parliamentary elections.
On Sunday, Morsi's Muslim Brotherhood group and its allies stepped up confrontations in the streets ahead of the vote. Students at Cairo and Ain Shams universities marched off campus, burned tires and blocked main roads. Riot police fired tear gas and students responded by hurling stones. In one incident, witnesses say the students set a police vehicle and a traffic post on fire.
Students at the Islamic Al-Azhar University also protested. Police arrested 19 protesters for blocking traffic, said a security official who spoke on condition of anonymity because he was not authorized to brief reporters.
Some fear violence could mar the vote. The military and police will deploy hundreds of thousands of soldiers and officers -- including special forces commandos -- to guard the vote. The official Facebook page of military spokesman Col. Ahmed Mohammed Ali showed an image Sunday of army chief Gen. Abdel-Fatah el-Sissi inspecting troops who will be on duty for the election.
Mansour also ordered a change to Egyptian law to now punish those found guilty of illegally casting a ballot with up to 15 years in prison.
In his speech to the nation ahead of the birthday of Prophet Muhammad, Egypt's interim president said the constitution "paves the way to serious and steady steps toward democracy." Mansour also said that Egyptians should "strike an example in civilization and commitment to the world."
In a voice choked with tears, Mansour hailed both police and armed forces by recalling a verse from the Quran that gives blessings to those who "spend the night guarding in the sake of God." He also criticized Islamic extremists who twisted Islamic teachings to "unleash the machine of killings," a reference to the monthslong campaign of suicide bombings and attacks targeting security forces.
The government has designated the Brotherhood a terrorist group and blamed it for the rising attacks. The Brotherhood, which renounced violence in the late 1970s, denies being behind the violence. However, protests by its supporters often turn violent and security forces killed hundreds when raiding two pro-Morsi sit-ins in August.
Ahead of the vote, the Interior Ministry accused the Brotherhood of trying to "lure the poor and the impoverished who live in the slums" by taking their IDs in exchange for food and blankets -- a means to stop them from voting. The Brotherhood claimed on its website that the government was offering the equivalent of $70 to the poor if they promise to vote for the constitution.
Meanwhile, the retrial of Egyptian autocrat Hosni Mubarak, forced out of power in the country's 2011 revolution, has been postponed to Feb. 8. He faces charges over the killing of protesters at the end of his rule.
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