Security officials say an explosion has hit a public bus in the Egyptian capital Cairo, wounding five people.

The officials say the blast went off Thursday morning as the bus passed through Cairo's eastern Nasr City district. They said the cause was still uncertain but they suspected an explosive device was thrown at the bus or set nearby. The officials spoke on condition of anonymity because they were not authorized to talk to the press.

Egypt has seen a wave of attacks blamed on Islamic militants since the July military ouster of Islamist President Mohammed Morsi and the subsequent crackdown on his Muslim Brotherhood group. On Tuesday, a suicide car bomber struck a police headquarters in the Nile Delta city of Mansoura, killing 15 people, in the worst bombing yet.