Two police officers were wounded on Sunday when an explosive device went off in Egypt's capital Cairo, state-run Al-Ahram news website reported.
The blast targeted a Central Security Forces position outside a sports club in eastern Cairo, security sources were quoted as saying.
Tensions escalated during the past days as Egypt marks the fourth anniversary of the January 25 uprising which toppled president Hosni Mubarak.
On the eve of the anniversary, an Egyptian female protester was shot dead in downtown Cairo as police dispersed a leftist march heading towards the iconic Tahrir Square.
According to official MENA news agency, the Tahrir Square has been completely closed since late Saturday. At least 22 army vehicles have been deployed at the entrances of square, which is sealed off by barbed-wires.
Armed security men are patrolling the streets in downtown Cairo and neighboring governorates amid calls for mass demonstrations.
January 25 is a national holiday marking the start of 18-day nationwide protests against Mubarak in 2011. The death of Saudi King Abdullah cancelled planned celebrations of the day.
The 2011 popular uprising toppled Mubarak and brought the Muslim Brotherhood's Mohamed Morsi to office in 2012, who was later ousted by the military in July 2013 after mass protests against his one-year rule.
Egyptian President Abdel-Fattah al-Sisi, who led Morsi's removal as military chief then, made a statement on Saturday and referred to the anniversary of January 25 uprising as "a new torch for hope, progress and action."