Fresh clashes have broken out in the Egyptian capital Cairo in the worst violence since President Mohammed Mursi took office at the end of June.
At least 12 people were injured when supporters and opponents of Mr Mursi fought each other in Tahrir Square.
Tensions are high after Egyptian judges criticised Mr Mursi’s attempt to remove the country’s top prosecutor.
It follows the acquittal of 24 people accused of attacks on protesters during last year’s uprising.
Witnesses said a rally critical of the president was taking place in Tahrir Square on Friday when a crowd of his supporters stormed their stage.
Fighting broke out and protesters pelted each other with stones, a hospital official told the official Mena news agency.
As darkness fell at least one bus, believed to belong to the Muslim Brotherhood, was seen on fire near the square.
The BBC’s Jon Leyne in Cairo says that, 100 days into his term, this is the first time President Mursi, who is backed by the Muslim Brotherhood, has experienced a big demonstration against him.
His opponents are angry at Egypt’s proposed new constitution which they see as too dominated by Islam, he says.
They say the president has failed to live up to his promises.
The counter demonstration by the president’s supporters was organised under the pretext of complaining about the recent court verdict, our correspondent adds.
Angry response
Earlier, a group of Egyptian judges criticised President Mursi’s attempt to remove the country’s top prosecutor as a “farce”.
The president said he was reassigning Prosecutor-General Abdel Maguid Mahmoud – regarded as a figure from the era of ousted President Hosni Mubarak – as Vatican envoy.
Mr Mahmoud is refusing to go.
The move against Mr Mahmoud followed an angry public response to the acquittal of the 24 people who had been accused of sending men on camels and horses to break up a protest in Cairo in 2011, leaving several people dead.
Those accused included Fathi Sorour and Safwat al-Sherif, former speakers of Egypt’s two houses of parliament.
Prosecutors said Mr Sherif, who was also the secretary general of Mubarak’s National Democratic Party (NPD), had “contacted MPs, members of the NDP and financiers of the party, inciting them to disperse the protests in Tahrir Square by force and violence”.
The case is the latest flashpoint between Mr Mursi’s government and figures associated with the Mubarak era.
