After participating in a public prayer with 2000 people, opposition figure Mohamed ElBaradei and other protesters clashed with police in Giza.
ElBaradei and followers conducted the public prayer after finding Mostafa Mahmoud Mosque in Mohandiseen closed, according to Al Jazeera.
The controversial leader, who traveled to Egypt from Vienna Thursday, has offered to head an interim government.
Thousands of activists also clashed with security forces outside of Al-Azhar Mosque in Islamic Cairo after Friday prayers, according to AFP.
Hundreds of security forces blocked traffic into downtown Tahrir Square, surrounding the area where 30,000 protesters gathered Tuesday to demand economic and political reform.
State security official said during an interview with Al Jazeera that people would be allowed to peacefully express their opinions, providing they cooperate with police.
Plainclothes officers stopped people walking toward Tahrir, yelling at them and interrogating them.
North of Cairo in the Mediterranean city Alexandria, police fired rubber bullets and tear gas at protesters who rallied after prayers. There have been unconfirmed reports of casualties from the violence.
Demonstrators also gathered in Damietta, Fayoum, Suez, Damnhour in the Nile Delta, Minya in Upper Egypt, and Arish in Sinai.
Internet and phone service is still down and TV channel Al Jazeera Live has been blocked from broadcasting on NileSat.
