Egyptian security forces said they have arrested a man suspected of leading an al-Qaeda-linked group in an ambush where 25 off-duty policemen were lined up and shot last week on the Sinai peninsula.
The man, Adel Mohammed, also known as Adel Habara according to one official, has already been sentenced to death in absentia for killing soldiers in the Nile Delta last year.
Habara's arrest, announced on Saturday, could potentially undermine armed groups in the area, where over two dozen security men have been killed alone since July.
The security official said two other suspects were arrested along with Habara.
Earlier on Saturday, security officials said 31 suspected fighters have been arrested since Thursday, including three suspected of involvement in last week's attack and two caught seeking treatment for wounds sustained in clashes with police.
Attacks against security forces on the peninsula have increased since a July 3 military coup deposed President Mohamed Morsi.
In the latest attack, gunmen killed a police officer on Friday, according to the Interior Ministry.
The riot police officer was shot in the chest while on patrol in the city of El-Arish, the ministry said.
Since the ouster of Morsi, his supporters have been organising regular protests calling for his return. Several thousand took to the streets on Friday.
Health Ministry spokesman Khaled el-Khateeb raised the death toll in violence during Friday's protests to eight, and added that 221 people were injured, most of them in clashes between Morsi supporters and local residents.
Those killed included one police officer and one civilian shot dead in a drive-by shooting targeting a police station in an upscale neighbourhood of Cairo.