A pair of suspected militants on Sunday killed a policeman in the coastal city of El-Arish in northern Sinai.
Army troops also fired on a car near the border with Gaza.
Gunmen inside the vehicle returned fire before they fled the scene.
At least 10 explosive devices prepared to be remotely detonated were found in the car, according to security officials.
They spoke on condition of anonymity because they were not authorized to speak to the media.