But Reuters quoted a cabinet spokesman denying any government effort to mobilize supporters of President Hosni Mubarak against the protesters. "We were surprised with all these actions," spokesman Magdy Rady told the wire service. "To accuse the government of mobilizing this is a real fiction. That would defeat our object of restoring the calm."
And there was more bloodshed Thursday. Protest organizers said Mubarak loyalists opened fire on demonstrators before dawn. Sporadic clashes continued through the morning, though for the most part the pro- and anti-government groups kept their distance from each other, often on opposite sides of a line of military vehicles or personnel.
Refusing government requests for them to end their 10-day old demonstration, protesters set up makeshift hospitals in alleyways off the square to treat the wounded, and fashioned a holding cell in a nearby travel office to detain those they suspected of inciting the violence.
Organizers said they had captured more than 350 "thugs of the government" among the pro-government demonstrators, some carrying police identification cards, and turned them over to the Egyptian army.
"Mubarak told them to kill us," said Osama Hilal, 27, a doctor who was treating the wounded at a makeshift triage center. "He thinks he can succeed to make all the people get out of this square. But we will not leave."
Human Rights Watch condemned the Egyptian government for what it called "organized attacks on pro-democracy demonstrators" Wednesday and asked that those responsible be prosecuted.
"The events in Tahrir Square and elsewhere strongly suggest government involvement in violence against peaceful protesters," said Kenneth Roth, executive director of the watchdog group. "The U.S. and other allies should make clear that further abuse will come at a very high price."
Also Thursday, the United Nations announced that it was evacuating 350 staffers from Egypt, as protesters vowed to continue efforts to oust Mubarak. And Britain, France and Germany issued a joint statement calling on Mubarak "to avoid at all costs the use of violence against unarmed civilians, and on the demonstrators to exercise their rights peacefully."
In Washington Wednesday, White House spokesman Robert Gibbs called the violence "outrageous and deplorable" and warned that if any of it was "instigated by the government, it should stop immediately."
The violence came after the army had urged pro-democracy demonstrators to go home early Wednesday, saying Mubarak's pledge the previous night to hand over power this fall showed that their voices had been heard. The coordinated nature of Wednesday's events suggested that his supporters were determined to show, as Mubarak had warned, that the country faced a "choice between chaos and stability."
Thousands of Mubarak supporters, whipped up by state television and spoiling for a fight, flooded into Cairo's downtown at midday. They engaged in a pitched battle with Mubarak's opponents on a street alongside the Egyptian Museum, while the army mostly stood by.
The president's supporters fueled the showdown with a charge by men riding camels and horses, wielding whips and clubs. Both sides then went at it with rocks, sticks and firebombs. Hospitals reported that three people had been killed Wednesday and more than 600 injured.
Mubarak's opponents said they would not back down from their quest to force him from office. But Mubarak loyalists seemed to be pushing back with new vigor. Omar Suleiman, the new vice president, said Wednesday that there would be no dialogue with the opposition until the protests stopped, while Egypt's Foreign Ministry said that calls from Washington and other capitals for Mubarak's swift exit were intended to "incite the internal situation" in the country.
By Thursday, the square was filled once more with anti-Mubarak demonstrators, and the mood had definitively shifted. Where once a popular slogan was, "We're going to stay in the square," now it is, "We're going to die in the square."
Volunteers transformed a mosque into a hospital, emptying bookshelves of holy texts in order to stack bandages, gauze and antiseptic. At the travel office, demonstrators used plastic wrist restraints to handcuff Mubarak loyalists hauled into custody, and showed reporters police identification cards that had been found on some of those allegedly inciting violence.
Saal el Ravi, a doctor working at the makeshift hospital, said the five who were fatally shot arrived between 3:30 and 5:30 a.m., he said. Dozens of others were treated for less serious gunshot wounds, he said. Doctors said hundreds of others came in with head and body wounds caused by rocks, fists and sticks.
"They were killing our people," said Arafat Hussein, 25, a worker at the Ministry of Health who said pro-Mubarak forces fatally shoot two of his friends--one in the head, the other in the heart, he said. He had recovered a shell casing, which he said had been fired by a Kalishnikov rifle. He showed it to anyone willing to stop and look.
Nearby, in an abandoned travel agency office, anti-government protesters had created a temporary jail. Angry mobs were bringing in captives, including several whose identification cards said they were police officers or members of Mubarak's National Democratic Party.
One heavy-set captive denied he was with the police, but his jailers said a card found on him identified him as Major Osama Kamal Mohamed, of the Interior ministry. Mohamed's jailers lifted his arms up behind his back, trying to get him to confess, and he cried out in pain. A protester called him a "drama queen." Another, dentist Ibrahim al Hakim, said, "This is what they would do to us."
Mubarak's supporters, seemingly energized by his announcement Tuesday, essentially laid siege to Tahrir Square Wednesday, where for nine days protesters calling for the president's ouster have claimed the attention of Egypt, the Middle East and the rest of the world.
Anchors on state-run television heavily promoted the "pro-stability" rally, and buses and trucks dropped off loads of government backers at sites downtown. The owners of a factory said they had been told by the ruling National Democratic Party to mobilize their workers for the demonstration, a move that has been a standard practice here for decades. Many who took to the streets appeared to have come prepared for the vicious fight that ensued.
The Internet, which had been cut off for most of the past week, came back on in late morning; some anti-government demonstrators suspected that it was used to help coordinate the counter-rally. The night before, the army had sent text messages to Egyptians calling on them to protect their country from destruction.
Pro-democracy demonstrators alleged that their foes were paid to take to the streets by the ruling party, by the police or by wealthy businessmen with deep ties to the government. All of those elements, the protesters say, are sufficiently desperate to take extreme measures.
The Interior Ministry denied the accusation, and interviews with those who turned out in favor of Mubarak suggested that they genuinely support him.
The Obama administration avoided accusing Mubarak's government of directly authorizing the attacks, but one senior administration official in Washington described the onslaught as "classic ruling-party behavior."
The thousands of Mubarak supporters who participated were boisterous and aggressive. Frequent chants attacked pro-democracy leader Mohamed ElBaradei as an American puppet, and al-Jazeera, the satellite television network based in Qatar, as a tool of Iran. Journalists who were thought to be working for al-Jazeera were threatened or roughed up.
But their dedication to the cause didn't seem to match that of their opponents; as the evening wore on, their numbers dwindled sharply. The battle diminished, and the anti-Mubarak protesters continued to occupy the square.
Some Mubarak supporters praised him as the father of the nation and said they couldn't imagine Egypt, the Arab world's most populous country, without him. "We're behind you whatever you say, wherever you go," said one sign.
But others offered a more complicated motivation. Gamal Abu el-Ela said he sympathized with the anti-government protesters. "But this uprising has succeeded and delivered its message," he said. "We want freedom and transparent elections, but now we have to give the ruling party the chance to implement this reform."
And some were touched by Mubarak's avowal, in his Tuesday night address, that he would die in Egypt. Gamal Hamzan, an emergency room doctor at Kasr El Aini Hospital, said that Mubarak, 82, is an old man and that it is un-Egyptian to insult the elderly.
Rocks and firebombs
Just after 1 p.m., Mubarak supporters, who had been pouring into the center of Cairo since late morning, rushed through security checkpoints that had been set up by protesters at Tahrir Square. They chanted pro-Mubarak slogans and pushed forward. Pro-democracy demonstrators nearby held up a sign that read "Welcome to Martyrs' Square," in a nod to the more than 150 people who had been killed in the past nine days.
The scene quickly turned violent as the two camps confronted each other. Supporters of the government, some carrying sticks, threw rocks into the crowd of their rivals, who threw rocks back as people rushed in every direction.
Women and children ran for cover. A teenage boy carrying koshari, a traditional Egyptian dish, was beaten for taking food to critics of Mubarak.
Eventually, members of the military fired into the air to disperse the crowd. Two military vehicles were used to separate the demonstrators, but rock-throwing continued.
In the evening darkness, gasoline bombs came dropping down from the roof of an 11-story building across the street from the Egyptian Museum - apparently from the hands of anti-Mubarak protesters. Other firebombs fell from a shorter building next door, which seemed to be held by their opponents. Sometimes the two groups lobbed bombs at each other.
Their flames glowed brilliantly in the night, and they sent dark smoke into the air, but it was difficult to tell if they did much damage. The sounds of gunfire and explosions continued late into the night.
Mohammed Shahad, who was in the pro-government group, said unprompted, "Nobody told me to come here. Nobody paid me to come here."
"Mubarak is the only person of honor in this country," he added. "The only person that can save this country."
Wilgoren reported from Washington. Staff writer Joby Warrick in Washington contributed to this report.