Violence has broken out and officials have reported deaths at several Muslim Brotherhood demonstrations across Egypt. This comes days after hundreds died when security forces cleared two pro-Morsi camps in Cairo.
The protesters poured out onto the streets of the capital and other cities following Friday Muslim prayers in the early afternoon.
Television footage showed thousands of demonstrators marching across one of the bridges over the Nile in Cairo, chanting slogans in support of the Muslim Brotherhood and ousted President Mohammed Morsi.
This came in response to the Muslim Brotherhood's call for a "day of rage," to protest against Wednesday's deadly clashes, which ensued when security forces moved in to forcibly break up two sit-ins in Cairo.
Armored military vehicles had sealed off main squares and junctions in several parts of the capital in anticipation of Friday's demonstrations.
The Muslim Brotherhood said 25 people had died in clashes at Ramses Square in Cairo. However, Egyptian officials have not confirmed that number.
Elsewhere, in the Suez Canal city of Ismailiya, at least four people were reported killed in clashes between Islamist protesters and police. The health ministry also reported eight dead in the Nile Delta province of Dumyat, which lies about 200 kilometers (124 miles) north of Cairo.
In the southern city of Fayyoum, health and security officials said at least five people had died in violent demonstrations.
The demonstrations come in defiance of a state of emergency imposed by the military following Wednesday's violence, in which 638 people were killed.
They also come just hours the United Nations Security Council called on all parties in Egypt to exercise maximum restraint.
"The view of Council members is that it is important to end violence in Egypt," Argentine U.N. Ambassador Maria Cristina Perceval said after a meeting at UN headquarters late on Thursday.
Muslim Brotherhood supporters and the military have been at loggerheads ever since the military ousted democratically elected Islamist President Morsi and installed its own civilian government on July 3.
pfd/kms (AP, AFP, dpa)