Egyptian security forces are fighting gunbattles in a town near Cairo after launching an operation targeting "criminal and terrorist hotbeds".
State media report a senior policeman died in clashes with militants in Kerdasa and at least 28 suspected militants have been held.
But several hours after the operation started, security forces were having to take cover from gunfire.
Eleven police officers were killed at a police station in Kerdasa last month, weeks after the overthrow of Islamist President Mohamed Morsi in July.
Soldiers went into Kerdasa at about 5:30am local time, backed by helicopters.
Residents told the BBC that security forces were searching homes in Kerdasa for members of Mr Morsi's Muslim Brotherhood movement.
