Fresh clashes broke out in Cairo on Friday in the worst trouble since President Mohammed Mursi took office at the end of June.
More than 40 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 Prosecutor-General Abdel Maguid Mahmoud after 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, bottles and petrol bombs.
The Mena news agency reported 41 people had been treated for injuries.
The BBC says this is the first time President Mursi has experienced a big demonstration against him.
The president said on Thursday he was reassigning Mr Mahmoud - who is regarded as a figure from the era of ousted President Hosni Mubarak - as Egypt's envoy to Vatican. Mr Mahmoud is refusing to go.