Allies and foes of Egypt's Mohamed Morsi lobbed firebombs and rocks at each other on Wednesday as their simmering standoff over the Islamist president's expanded powers and a new constitution turned violent.
Bloodied protesters were seen being carried away as gunshots could be heard and the rivals torched cars and set off firecrackers near the presidential palace, where opponents of Morsi had set up tents before his supporters drove them away.
Riot police were eventually deployed to break up the violence, but clashes were still taking place in side streets near the palace in the upscale Cairo neighbourhood of Heliopolis.
The health ministry said 211 people had been injured so far.
Sunni Islam's highest authority, based in Cairo, called for restraint and dialogue, as did the United States and Britain.
"It's a civil war that will burn all of us," said Ahmed Fahmy, 27, as the clashes raged behind him.
"This is a failure of a president. He is waging war against his own people," 56-year-old Khaled Ahmed told AFP near the palace.
At the heart of the dispute is a decree by Morsi, in which he took on sweeping powers, and the hasty adoption of a draft constitution in a process boycotted by liberals and Christians.
But despite the deadly protests and strikes prompted by the decree two weeks ago, 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.
"There is a real political will to respond to the demands of the opposition," Mekki told journalists.
The clashes erupted after thousands of Islamists rallying to the call of the Muslim Brotherhood bore down on the palace, tearing down the opposition tents.
The two sides threw stones at each other before secular-leaning opposition protesters, who had besieged the palace in their tens of thousands on Tuesday, escaped into side streets.
Prominent opposition leader and former UN nuclear watchdog chief Mohamed ElBaradei said Morsi bore "full responsibility" for the violence and that his regime was losing more legitimacy every day.
He said the opposition, jointly led by former Arab League chief Amr Mussa and ex-presidential candidate Hamdeen Sabbahi, was ready for dialogue but only if Morsi rescinds the decree.
"There is no legitimacy in excluding the majority of the people. There is no legitimacy in enabling one group to dominate Egypt," he said in reference to the Brotherhood, on whose ticket Morsi ran for office.
He added the opposition would used "any means necessary" to bring down the charter, but stressed that all methods would be peaceful.
Meanwhile, three of Morsi's advisers resigned over the crisis, state news agency MENA reported, naming Amr al-Laythi, Seif Abdel Fattah and Ayman al-Sayyad.
Earlier Islamist rallies converged outside the palace, where hundreds of anti-Morsi protesters had spent the night.
"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 opposition protesters ran away as they can't face our strength."
Sunni Islam's highest authority, Al-Azhar Grand Imam Ahmed al-Tayyeb, urged "all Egyptians of all persuasions to exercise restraint and to recourse to peaceful and civilised dialogue".
He described the crisis as a "disaster," MENA reported, and urged "officials from the opposition and the government to begin dialogue as soon as possible... in order to save Egypt."
As the country faces its most divisive crisis since Morsi took power in June, 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.
For his part, British Foreign Secretary William Hague called for all sides to "show restraint", and urged the authorities to "make progress on transition in an inclusive manner which allows for a constructive exchange of views."
Morsi insists the measures are aimed at cutting short a tumultuous transition. Opponents have accused him of seeking to become a dictator.