The explosion on Saturday morning has wounded five people, including two police officers, medics at the scene told AFP news agency.
Egypt`s public prosecutor, Hisham Barakat, was killed last month by a car bomb attack in the city.
In the same month, another car bomb targeting a police station left three people dead.
Egyptian security forces have been battling Islamic militants, but the fighting has been mostly confined to the Sinai Peninsula.
Militants in Egypt have killed at least 600 police and armed forces personnel in the past two years.
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