An Egyptian morgue official says the death toll has climbed to 35 during the third straight day of violence that has turned into the most sustained challenge yet to the rule of Egypt's military.

Most of the deaths were in the area around Cairo's central Tahrir Square, the epicenter of the uprising that ousted former President Hosni Mubarak in February.

On Monday, young activists demanding the military hand over power to a civilian government skirmished with black-clad police, hurling stones and firebombs and throwing back the tear gas canisters being fired by police into the square.

The official said 20 people had been killed Monday. He spoke on condition of anonymity because he was not authorized to brief the media.