Security sources in Egypt say four soldiers were killed and nine wounded when gunmen attacked a military bus on Sunday in the Sinai Peninsula.
Sinai-based militants have stepped up violence against the state since the ousting of Islamist President Mohamed Mursi in July.
Meanwhile the country’s health ministry says 49 people were killed in Saturday’s clashes during protests on the third anniversary of the uprising that toppled Hosni Mubarak from power.
Nearly 250 were wounded in Cairo and other provinces, according to the government.
The interior ministry says more than a thousand people it calls “rioters” were arrested and a number of policemen injured.
The trouble came as police broke up anti-government rallies.
In Cairo’s Tahrir Square it was a different story. Thousands turned out for a demonstration which had official support, hailing Egypt’s army chief General al-Sisi and the military-backed authorities.
The contrasting scenes highlight the deep divisions in the country following first the ousting of the dictator Mubarak, and last year’s removal of the elected President Mursi.