Gunmen have killed five Egyptian soldiers in an attack on an army patrol near the Suez Canal city of Ismailia, security officials said.

The attack took place north of the city, where suspected militants have repeatedly targeted security forces in recent weeks, the officials said.

Ismailia and the areas around it have seen regular attacks on police and military personnel, especially since the military toppled Islamist president Mohamed Morsi on July 3.

More than 100 policemen have been killed across Egypt in attacks and clashes since Mr Morsi was ousted.              

Meanwhile officials said a massive explosion had hit a security headquarters in a southern Sinai town.

On Sunday clashes in Cairo between security forces and Islamist protesters left 51 people dead.

Street battles raged for hours after supporters of Mr Morsi and backers of the military that deposed him poured into the streets and turned on each other.

It was the highest death toll in a single day in violence in Egypt since August 14, when security forces raided two sit-in protest camps by Mr Morsi's supporters in Cairo, killing hundreds.