Allies and foes of Egypt's Mohamed Morsi have lobbed fire bombs and rocks at each other as their simmering standoff over the Islamist president's expanded powers and a new constitution turned violent.
Bloodied protesters were seen carried away as gunshots could be heard and the rivals torched cars and set off fire crackers near the presidential palace on Wednesday, 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 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.
The violence 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.
As scattered clashes carried on into the night, the Brotherhood urged protesters on both sides to withdraw, as did Prime Minister Hisham Qandil.
The Brotherhood's Mahmud Ghozlan told AFP the protesters 'should withdraw at the same time and pledge not to return there given the symbolism of the palace.'
Earlier, the prestigious Islamic institution Al-Azhar, 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.
'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.'
At the heart of the dispute is a decree by Morsi, in which he took on sweeping powers, and the hasty subsequent adoption of a draft constitution in a process boycotted by liberals and Christians.
But despite the protests prompted by the decree two weeks ago, Vice President Mahmoud 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 said.
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.
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.
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.
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'.