Egypt's army deployed tanks outside the presidential palace on Thursday after five demonstrators died overnight in clashes between supporters and opponents of Islamist President Mohamed Morsi.
Morsi was expected to issue a statement on Thursday to address the worst violence since his June election, which has pitted Islamists against an opposition that has escalated protests since he assumed extensive powers on November 22.
Running street battles that carried on through the night outside the Itihadiya palace in northern Cairo also left 350 people wounded, many from buckshot, the official MENA news agency reported.
The opposition has said it would organise further marches to the palace as a top presidential aide accused them of coordinating with loyalists of deposed dictator Hosni Mubarak.
Morsi is expected to "reveal that facts and call for a dialogue," the head of his office Refaa Al-Tahtawy told the official Al-Akbar newspaper.
The stage was set for Wednesday's violence when Morsi's Muslim Brotherhood movement announced a march to the palace, where opposition protesters were staging a sit-in a day after tens of thousands surrounded the sprawling complex.
The protesters threw fire bombs and rocks at each other on Wednesday as their simmering stand-off over the president's expanded powers and a draft constitution turned violent.
Bloodied protesters were seen carried away as gunshots rang out and the rivals torched cars and set off fire crackers near the palace, where opponents of Morsi had set up tents before his supporters drove them away.
Riot police were eventually sent in to break up the violence, but clashes still took place in side streets near the palace in the upscale neighbourhood of Heliopolis.
The opposition says it will not stand down until Morsi discards his new powers, which allow him to take decisions uncontested by courts, and cancel a snap December 15 referendum on a new constitution opposed by liberals and Christians.
In the early hours of Thursday, gunshots rang out intermittently and sporadic violence continued, an AFP correspondent said.
Later in the morning, a few hundred Morsi supporters remained outside the palace. The opposition protesters had left the scene.
The overnight violence had also spread beyond the capital, with protesters torching the offices of the powerful Muslim Brotherhood in the Mediterranean port city of Ismailiya and in Suez, witnesses said.
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Sobhi Saleh, a Brotherhood official and member of the constituent assembly -- the body that drafted the controversial charter -- was attacked and beaten by opposition protesters in the northern city of Alexandria, MENA reported.
The Brotherhood urged protesters on both sides to withdraw, as did Prime Minister Hisham Qandil.
"It's a civil war that will burn all of us," said Ahmed Fahmy, 27, as the clashes raged behind him.
"They (Islamists) attacked us, broke up our tents, and I was beaten up," said Eman Ahmed, 47. "They accused us of being traitors."
Activists among the Islamist marchers harassed television news crews, trying to prevent them from working, AFP reporters said.
Wael Ali, a 40-year-old Morsi supporter with a long beard, said: "I'm here to defend democracy. The president was elected by the ballot box."
The United States called for an open and "democratic dialogue".
"The upheaval we are seeing... indicates that dialogue is urgently needed. It needs to be two-way," US Secretary of State Hillary Clinton said in comments echoed by Britain and the European Union.
Despite the protests , Vice President Mahmud Mekki said a referendum on the charter "will go ahead on time" as planned on December 15.
The opposition would be allowed to put any objections they have to articles of the draft constitution in writing, to be discussed by a parliament yet to be elected.
Prominent opposition leader and former United Nations nuclear watchdog chief Mohamed ElBaradei said Morsi bore "full responsibility" for the violence.
He said the opposition was ready for dialogue but they would use "any means necessary" to scupper the charter, but stressed that these would be peaceful.
Meanwhile, three of Morsi's advisers resigned over the crisis, MENA reported, naming Amr al-Laythi, Seif Abdel Fattah and Ayman al-Sayyad.