Two separate improvised explosive devices in Egypt's coastal city of Alexandria injured two civilians and two policemen, while police dispersed a number of small protests elsewhere on Friday.
An improvised bomb exploded in front of gate eight of the El-Dekhela Port, injuring a passerby and a driver, and also causing damage to the driver's car, Al-Ahram Arabic website reported.
Another bomb exploded west of Alexandria, targeting a police vehicle and injuring a police officer and a conscript. The two policemen sustained minor injuries.
Meanwhile, security forces in Egypt's Sharqiya governorate dispersed three separate pro-Muslim Brotherhood protests using teargas. Eleven of the protesters were also arrested.
Similarly in Cairo's 6 October satellite district, police dispersed tens of pro-Brotherhood protesters following Friday prayers.
Pro-Muslim Brotherhood protests have taken place regularly, usually on Fridays, since the ouster of the Brotherhood-hailed Mohamed Morsi in July 2013.
The cabinet labelled the group a terrorist entity in December 2013, and has also issued a controversial protest law that requires protesters to notify the interior ministry at least three days before their protests to avoid hefty fines and prison sentences.
The two measures have contributed to the imprisonment of a large number of Morsi supporters as well as liberal activists.
The country has witnessed a number of explosions in the past week, mainly targeting electricity pylons and railway tracks, as the country marked the fourth anniversary of the 25 January uprising that ousted autocrat Hosni Mubarak.
Security was tightened on Friday after a deadly militant attack in North Sinai the day before left at least 30 dead, including army personnel and civilians.
Egypt's army has been waging a fight against a decade-long militant insurgency in the peninsula that has spiked in the past year and a half.
Attacks have mostly targeted army and police personnel, but civilians have been affected too.
These attacks have at times spread to Cairo and its surrounding governorates.