A powerful explosion shook central Cairo Friday morning killing at least four people and wounding dozens more, state television reported.

State news agency MENA quoted an unnamed security official as saying the explosion was caused by a car bomb outside the police building.

The explosion sent a large plume of smoke rising over the city center and there were reports of gunfire in the area just after the blast.

Meanwhile, three other bombs exploded in different parts of the city.

Hours after the first attack, a crude explosive device targeting police vehicles near a metro station killed one person and injured at least 15 others.

A short time later, a third bomb exploded near a police station in the west Cairo Talebiya district, which is located near the famous Giza Pyramids. According to officials, the home-made device caused no casualties.

The fourth blast also occurred near outside of a movie theater in the same part of Cairo, according to local authorities, killing one person as a convoy of security forces passed by.

No one has claimed responsibility for the attacks but the country has seen a sharp rise of violence against security personnel since the army ousted Islamist President Mohammed Morsi in July.

The blasts come one day after five policemen were killed in an attack in the city of Beni Sueif, south of Cairo.

The attacks also come on the eve of the three year anniversary of the 2011 uprising that toppled Egypt's longtime autocratic ruler Hosni Mubarak.

hc/rc (Reuters, AFP, AP, dpa)