Two Egyptian policemen have been killed and two others injured in two blasts in northern Sinai, officials said.
Thousands of police have been brought in for the hunt
The interior ministry said police were operating in Jabal Halal when the booby-trapped devices exploded.
It was the second such incident in the area in two days, and came as security forces searched for militants suspected in several recent bomb attacks.
It is not clear if the devices were freshly planted or date back to past conflicts in Sinai with Israel.
An explosion thought to have been from a landmine damaged an armoured car and wounded at least three policemen on Wednesday.
Hundreds of people are reported to have been arrested since Tuesday, when about 3,500 police began their search.
The Jabal Halal area is full of caves and valleys, some of which are said by officials to have been booby-trapped by a key suspect in last month's Sharm al-Sheikh resort bombings and attacks in eastern Sinai last year.