Amr Nabil, Associated Press
Canadian volunteer nurse, Merikel, right, helps an Egyptian medical team to treat an injured protester at a field hospital at Tahrir Square in Cairo, Egypt, Monday, Nov. 21, 2011. Egyptian riot police clashed Monday with thousands of protesters demanding that the ruling military quickly announce a date to hand over power to an elected government.

CAIRO — 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.