Khaled Elfiqi / EPA

Supporters of Egypt's President Mohammed Morsi demonstrate in Cairo on Dec. 11.

Updated at 5:12 p.m. ET -- Egypt's army chief called for talks on national unity to end the country's deepening political crisis after a vital loan from the IMF was delayed and as thousands of opponents and supporters of Egypt's Islamist president flocked to key locations in the nation's capital four days before a nationwide referendum on a contentious draft constitution.

The meeting was scheduled for Wednesday afternoon.

"We will not speak about politics nor about the referendum. Tomorrow we will sit together as Egyptians," armed forces chief and Defense Minister Abdel Fattah al-Sisi said at a joint gathering of army and police officials.

An aide said President Mohammed Morsi had supported the call for talks. The Muslim Brotherhood announced it would be there, while the main opposition coalition said it would decide on Wednesday morning whether to attend.

Outside the presidential palace - where anti-Morsi protesters are demanding the Islamist postpone the vote on a constitution they say does not represent all Egyptians - there was skepticism tinged with some hope.

"Talks without the cancellation of the referendum - and a change to the constitution to make it a constitution for all Egyptians and not the Brotherhood - will lead to nothing and will be no more than a media show," said Ahmed Hamdy, a 35-year-old office worker.

But the fact that the army was calling such talks "is an indication to all parties that the crisis is coming to a head and that they need to end it quickly," he said.

The demonstrators began 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. It was unclear who was behind the pre-dawn attack.

The violence stoked tensions ahead of the mass demonstrations in Cairo by supporters and opponents of 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.

Egypt is rapidly approaching its own 'cliff'

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: Morsi, his Muslim Brotherhood and ultraorthodox Salafis on the one side, and liberals, leftists and Christians, on the other.

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.

In a further twist, Egypt's largest union of judges voted overwhelmingly on Tuesday afternoon to boycott supervising polling stations, which will likely cast significant doubt on the referendum's integrity, NBC News reported.  

Cracks in the opposition 
The dispute has 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 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.

PhotoBlog: Protests in Egypt continue despite Morsi's concession

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.

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Protesters dismantle a barbed wired fence guarding Cairo's presidential palace ahead of demonstrations on Tuesday evening.

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.

'Men don't have to worry about being caught': Sex mobs target Egypt's women

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.

Egypt army gets temporary power to arrest civilians ahead of referendum

Egypt's army chief called for talks on national unity to end the country's deepening political crisis after a vital loan from the IMF was delayed.

The meeting was scheduled for Wednesday afternoon.

"We will not speak about politics nor about the referendum. Tomorrow we will sit together as Egyptians," armed forces chief and Defense Minister Abdel Fattah al-Sisi said at a joint gathering of army and police officials.

An aide said Mursi had supported the call for talks. The Muslim Brotherhood announced it would be there, while the main opposition coalition said it would decide on Wednesday morning whether to attend.

NBC News' Ayman Mohyeldin, Reuters and the Associated Press contributed to this report.

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