The victims were one officer, a low-ranking policeman and two conscripts, security officials on condition of anonymity told the Associated Press.
No information has been revealed on the gunmen but regular security forces have been facing militancy from tribesmen as well as from terrorist groups among which the Islamic State group.
Attacks against forces have sky-rocketed since 2013 following removal of Islamist President Mohamed Morsi by current President al-Sisi, then minister of defense.
Tuesday, the army said it killed five militants during a military campaign in Central Sinai. The operation carried out by ground and air forces enabled to demolish an underground hideout and arrest three militants.
The army also said it seized a van carrying narcotics.