A police officer's private car was torched on Friday by unknown assailants in the city of 6 October on the outskirts of Cairo.
Earlier the same day, two improvised bombs were thrown at a Central Security Forces truck deployed on Giza Bridge in central Cairo, leaving six people injured.
Security was deployed early on Friday ahead of expected protests by supporters of ousted president Mohamed Morsi in several areas around Giza and Cairo.
Violence escalated between Morsi supporters and security forces since the violent dispersal of the two main sit-ins last August which left hundreds killed. Police and army have become frequent targets of militant attacks.