Clashes have raged on and off since police used batons and tear gas to try to disperse a sit-in in Tahrir on Saturday.

Protesters have brandished bullet casings in the square, but police deny using live fire. Medical sources at Cairo's main morgue said 33 corpses had been received there since Saturday, most of them with bullet wounds. At least 1,250 people have been wounded, a Health Ministry source said.

"I've seen the police beat women my mother's age. I want military rule to end," said 21-year-old Mohamed Gamal. "I will just go home in the evening to change my clothes and return."

Islamists dominated demonstrations against army rule on Friday, but the unrest in Tahrir since then has drawn in many of the young activists who helped topple Mubarak on February 11.

Army generals were feted for their part in easing him out, but hostility to their rule has hardened since, especially over attempts to set new constitutional principles that would keep the military permanently beyond civilian control.

Police attacked a makeshift hospital in the square after dawn on Monday but were driven back by protesters hurling chunks of concrete from smashed pavements, witnesses said.

"Don't go out there, you'll end up martyrs like the others," protesters told people emerging from a metro station at Tahrir Square, where about 4,000 had gathered by midday.