An Egyptian security official says an explosion has rocked a busy square in central Cairo, killing one police officer and causing panic. The official says the bomb detonated late Friday next to a traffic post in Lebanon Square in Cairo's Mohandessin district. Security forces sealed off the area while searching for more bombs, he said, speaking on condition of anonymity because he was not authorized to speak to the press. No group immediately claimed responsibility for the attack. Egypt has been hit with violence since the military overthrow of Islamist President Mohammed Morsi last year. An al-Qaida-inspired group, Champions of Jerusalem, has claimed responsibility for most of the deadly attacks, including the assassination attempt of Egypt's interior minister last year.