CAIRO (AP) -- Thousands of opponents and supporters of Egypt's Islamist president were flocking to key locations in the nation's capital ahead of rival mass rallies Tuesday, four days before a nationwide referendum on a contentious draft constitution.
The protesters were beginning to gather just hours after masked assailants set upon opposition protesters staging a sit-in at Tahrir Square, firing birdshot and swinging knives and sticks, according to security officials. At least 11 protesters were wounded in the pre-dawn attack, according to a Health Ministry spokesman quoted by the official MENA news agency.
The violence stoked tensions ahead of the mass demonstrations in Cairo by supporters and opponents of Islamist President Mohammed Morsi over the disputed draft constitution. The charter has deeply polarized the nation and triggered some of the worst violence since Morsi took office in June as Egypt's first freely elected president.
Protests are also planned elsewhere in Egypt, including the Mediterranean city of Alexandria and Suez to the east of Cairo.
The latest spate of violence in Egypt has divided the country into two camps: President Mohammed Morsi, his Muslim Brotherhood and ultraorthodox Salafis on the one side, and liberals, leftists and Christians, on the other.
It was unclear who was behind the pre-dawn attack on the protesters who have been staging a sit-in at Tahrir for nearly three weeks, the security officials said on condition of anonymity because they were not authorized to talk to the media.
The Tahrir protesters belong to the liberal opposition, which claims the draft of the charter restricts freedoms and gives Islamists vast influence over the running of the country. The draft, hurriedly adopted late last month in a marathon session by a constituent assembly dominated by the president's Islamist allies, is going to a nationwide referendum on Saturday.
The dispute prompted hundreds of thousands of the president's opponents to take to the streets in massive rallies - the largest from primarily secular groups since the uprising that toppled Hosni Mubarak last year. Morsi's supporters responded with huge demonstrations of their own, which led to clashes in the streets that left at least six people dead and hundreds wounded.
There have been at least two dozen attacks on offices of Morsi's Muslim Brotherhood, according to the group's leaders. Meanwhile, senior opposition figures, including former lawmakers, have been badly beaten by pro-Morsi Islamists.
Also in Cairo, several hundred Islamists were camped out Tuesday outside a media complex that is home to several independent TV networks critical of Morsi and the Brotherhood. The Islamists have threatened to storm the complex.
With four days left before the referendum, the opposition has yet to decide whether to campaign for a "no" vote or call for a boycott - something many see as a reflection of divisions within the opposition. The disparate opposition groups are led by reformist and Nobel Peace prize laureate Mohamed ElBaradei, Egypt's former foreign minister and Arab League chief Amr Moussa, and leftist politician Hamdeen Sabahi.
Cracks in the opposition's unity first appeared last weekend when one of its leading figures, veteran opposition politician Ayman Nour, accepted an invitation by Morsi to attend a "national dialogue" meeting. On Monday, another key opposition figure, El-Sayed Badawi of the Wafd party, met Morsi at the presidential palace.
The opposition has rejected any dialogue with Morsi until he shelves the draft constitution and postpones the referendum. They had also demanded that Morsi rescind decrees giving him near absolute powers. He withdrew those powers on Saturday, but insisted that the referendum will go ahead as scheduled.
Anticipating unrest on the day of the referendum, Morsi has ordered the military to join the police in maintaining security and protecting state institutions until after the results of the vote are announced. The decree went into effect on Monday.