Egypt is gearing up for rival demonstrations on the third anniversary of the uprising that toppled Hosni Mubarak.
Security has been tight around Tahrir Square in Cairo.
Supporters of the Muslim Brotherhood, which has called for peaceful protests, are expected to turn out in force – as are those of the military-backed government, which has vowed to clamp down on any attempt at “sabotage”.
A small bomb exploded near a police academy in Cairo on Saturday morning, reportedly injuring one person.
A group inspired by al Qaeda has claimed responsibility for a wave of attacks that killed six people on Friday.
At least another dozen were reported to have died in clashes between security forces and Muslim Brotherhood supporters.
Three years ago 30 years of Mubarak’s dictatorship came to an end after 18 days of often bloody protests which claimed hundreds of lives.
Last year more demonstrations led to the army’s overthrow of the elected Islamist President Mohamed Mursi.