The violent, chaotic scenes have brought to the fore the simmering tensions between the ruling military council that took power after Hosni Mubarak's ouster and activists demanding the generals transfer power immediately to civilians. The clashes also serve as a near repeat of the deadly street fighting between youth protesters and security forces in November that lasted for days and left more than 40 dead.

Early Saturday, hundreds of protesters hurled stones at security forces, who set up a concrete wall and barbed wire to seal off streets between Tahrir and the nearby Parliament building. Soldiers on rooftops pelted the crowds below with stones, prompting many of the protesters to pick up helmets, satellite dishes or sheets of metal to try to shield themselves.

Stones, dirt and shattered glass littered the streets downtown, while flames leapt out of the windows of a two-story building set ablaze near Parliament, sending thick plumes of black smoke into the sky.

Witnesses said soldiers wielding batons and dressed in riot gear then chased protesters through the streets and into Tahrir Square, which served as the epicenter of the uprising that toppled Mubarak in February. Footage broadcast on the private Egyptian CBC television network showed soldiers beating two protesters with sticks, repeatedly stomping on the head of one, before leaving the motionless bodies on the pavement.

Soldiers set fire to tents inside the square, and swept through buildings where television crews were filming from and confiscated their equipment and briefly detained journalists.

In one case, soldiers charged up the stairs of a hotel from which Al Jazeera TV was filming the turmoil below and demanded a female hotel worker tell them where the media crew was or else they would beat her up, a member of the Al Jazeera crew said. "The woman was screaming and saying I don't know," the crew member said. The soldiers, who were in plainclothes, found the Al Jazeera crew and threw their equipment from the balcony, including cameras, batteries and lighting equipment to the streets, landing on a sweet potato cart whose stove started a fire.

Egypt's prime minister defended the security forces' response. While he acknowledged that people have died from gunshot wounds, he denied the military and the police had fired at protesters.

Rights groups and activists, however, charge that the military is carrying on the practices of the old regime, including arresting and beating dissidents. Many Egyptians have grown increasingly frustrated with its handling of the country's transition period, and activists accuse the ruling generals of trying to hang on to power.