Clashes between police and protesting youths erupted near Cairo's Tahrir Square on Tuesday ahead of a mass rally against a decree by Islamist President Mohamed Morsi granting himself broad powers.
On the edge of the square near the US embassy in Cairo, teenagers threw rocks at police who responded with tear gas, an AFP reporter said.
In Tahrir itself, protesters took to the podium urging an end to the confrontation between the teenagers and the police, which threatened to spill into the square.
Marches are planned from across the capital into Tahrir - the epicentre of protests that toppled Hosni Mubarak last year - where the numbers are expected to swell after the end of the work day.
Demonstrations have also been called in several Egyptian provinces including Alexandria on the Mediterranean, in the Nile Delta and in central Egypt.
Around the capital streets were quiet Tuesday, with several schools closed for the day despite an education ministry statement saying that schools and universities would run as normal.
In Tahrir Square, activists who have been camping out since Friday hoisted banners on lamp posts slamming the Muslim Brotherhood, on whose ticket Morsi ran for office.
“The Muslim Brotherhood stole the revolution” read one banner. Another said the president was “pushing the people to civil disobedience.”
A new clinic was set up in the middle of the square, which was closed to traffic, while dozens of ambulances were parked nearby, an AFP reporter said.
On Thursday, Morsi issued a decree that allows him to “issue any decision or law that is final and not subject to appeal”, effectively placing him beyond judicial oversight.
The decree put him on a collision course with the judiciary and consolidated the long-divided opposition which accuses him of taking on dictatorial powers.
After a meeting on Tuesday with top judges aimed at defusing the dispute, Morsi stuck by his controversial decree, which has sparked the worst political crisis since his election in June.
There is “no change to the constitutional declaration,” presidential spokesman Yasser Ali told reporters at the end of the meeting.