In the predawn raid on the square, hundreds of soldiers beat protesters with clubs and fired into the air in the square, highlighting the rising tensions between protesters and the military leaders whom they praised in Tahrir two months ago when President Hosni Mubarak fell from power.

Several thousand protesters, some armed with sticks and other makeshift weapons, had moved back into the square by Saturday afternoon. They vowed not to leave until the defense minister, Field Marshal Mohammed Hussein Tantawi, resigns. Tantawi, a Mubarak appointee, leads the Supreme Council of the Armed Forces, which rules Egypt now and is made up of the military's top generals.

The confrontation could mark a key juncture in Egypt's upheaval. For weeks, protest leaders have been critical of the military's handling of the post-Mubarak transition and sought to pressure it to change, but both sides also worked to stay on good terms. Now the overnight clashes resembled the ugliest moments of the 18-day protest movement against Mubarak — with authorities cracking down on protesters and demonstrators chanting for the leader's removal.

Soldiers backed with a line of armored vehicles swept into the square around 3 a.m., firing continual barrages into the air with automatic weapons to intimidate protesters camped out in the center of Tahrir. The troops waded into the tent camp, where protesters had formed a human cordon to protect several army officers who had joined their demonstration in defiance of their superiors.

Witnesses reported two killed. Ali Mustafa, a car mechanic who was guarding the "free soldiers" tent, said he saw an attacking soldier stab one of the officers to death with his bayonet. He pointed to a section of pavement stained with blood under a small pile of garbage and food remains.

Another protester was shot dead, said Ahmed Gamal, who was there overnight and said he helped carry away the body. He added that he saw at least two others severely injured by live ammunition. The deaths could not be confirmed.

The Health Ministry issued a statement saying only one person was killed and 71 wounded, some of them with gunshot wounds, including three in critical condition.

Witnesses said the troops kicked the protesters and beat them with batons and fists and dragged an unknown number of protesters away and threw them into police trucks. Near the famed Egyptian Museum, which overlooks the square, protesters trying to flee were blocked by soldiers, who hit them and knocked them.

"I saw them detain a bunch at the museum. They were beating some pretty badly," said one protester, Loai Nagati.

As the sun came up Saturday morning, black smoke rose as protesters set fire to three vehicles in the square, including two troop carriers. The square was filled with shattered glass, stones and debris in a scene reminiscent of the protests that brought down Mubarak on Jan. 11. The glass storefront of a KFC on the square was also smashed.

"We are staging a sit-in until the field marshal is prosecuted," said Anas Esmat, a 22-year-old university student in Tahrir as protesters dragged debris and barbed wire to seal off the streets leading into the square.