Egypt's state television says a fourth explosion has hit the area outside the main campus of Cairo University. There was no immediate word on casualties in the latest blast.
- At Least Three Killed in Cairo as Brotherhood Supporters Protest
- Three Years On, Egyptians Fear Future Darker Than Mubarak Era
- UN Chief Tells Egypt He's Concerned by Mass Death Penalties
The explosion appeared to be much smaller than two bombings that struck at the same location on Wednesday, less than two hours earlier.
Those explosions killed at least two people — a police brigadier general and a civilian — and wounded seven, three senior police officers and four civilians.
The bombings targeted riot police routinely deployed at the location in anticipation of near-daily protests by students who support ousted Islamist President Mohammed Morsi and his Muslim Brotherhood group.
Egyptian state TV described the bombs as crude and homemade..
The officials spoke on condition of anonymity because they were not authorized to speak to the media.