More than 60 people were killed across Egypt on Friday in clashes between Islamist protesters and security forces, according to tolls from witnesses, security sources and the health ministry.
An AFP correspondent counted at least 19 bodies in one Cairo mosque, while eyewitnesses at a second mosque said more than 20 bodies of protesters were laid out.
One eyewitness said as many as 27 corpses were lined up inside the second mosque, in Cairo's Ramses Square.
Security sources said 27 people were killed in cities across the country, but gave no toll for Cairo, while the health ministry confirmed 22 deaths, also excluding the capital.
The counts put the toll from violence across Egypt on Friday at 66 dead.
The Muslim Brotherhood said 45 people had been killed in Cairo, accusing security forces of using live fire against peaceful protesters.
The health ministry said four people were killed in violence in the Suez Canal city of Ismailiya and another eight in northern Damietta.
Security sources also reported a police conscript was killed when gunmen attacked a checkpoint in the capital.
Among those killed elsewhere were a policeman in the North Sinai town of El-Arish, and one protester in the canal city of Port Said.
The violence came as Islamists marched in several cities around Egypt in what they dubbed a "Friday of anger" to protest the killing of hundreds of loyalists of ousted Islamist president Mohamed Morsi during a security crackdown on Wednesday.
Protests were held in Cairo, in the second city of Alexandria, in several Nile Delta provinces, in Suez canal cities and central Egyptian provinces.
The interior ministry said Thursday that it would take tough measures, including the use of live fire, if protesters attacked government buildings.