Gunmen shot dead three policemen in the northern Sinai Peninsula on Monday, Reuters' Aswat Masriya reported.
Security sources said unknown gunmen stormed a police station in the North Sinai city of Al-Arish and opened fire "intensely" at security personnel on duty, killing three. The assailants fled by car.
Other media reports said the policemen were ambushed while on their way to the police station.
The Egyptian army is carrying out a weeks-long air and ground assault in the sparsely populated peninsula, which borders Israel and the Palestinian Gaza Strip, to uproot Islamist militants who have intensified their activities against the police and army amid a security vacuum following the overthrow of long-time autocrat Hosni Mubarak in 2011.
There has been a spike in attacks on security personnel in Sinai since the military's popularly-backed ouster of Islamist president Mohamed Morsi on 3 July.
A military official, who spoke on condition of anonymity, told AP that elsewhere on Monday, gunmen opened fire at military checkpoints in the northern Sinai towns of Al-Arish and Sheikh Zuweyid, wounding a total of five soldiers and a civilian.
A Sinai-based militant group, Ansar Beit Al-Maqdis, has claimed responsibility for a failed assassination attempt against Egypt's interior minister on 5 September.
The military says it has killed dozens of Islamist militants, and captured hundreds of others during its operation targetting weapons caches and militant hideouts in the restive peninsula.