CAIRO — Barely 12 hours after Egyptian President Hosni Mubarak said he'd step down at the end of his term, a club-wielding mob chanting his name overwhelmed pro-democracy protesters in Tahrir Square on Wednesday, hurling stones and gasoline bombs at the people who've demanded that Mubarak resign immediately after nearly 30 years in power.
The apparently choreographed onslaught _ the pro-Mubarak forces had massed outside the square for hours and came equipped with slogans and knives _ opened a violent new chapter in Egypt's nine-day-old uprising and defied President Barack Obama's call for a transition to a new government.
The running battles continued for hours in the shadow of the famed Egyptian Museum, home to the country's priceless antiquities, whose rooftop one Mubarak supporter briefly used to lob Molotov cocktails at demonstrators.
By midnight it appeared that the democracy movement had regained control of the downtown Cairo square it's occupied since Jan. 25. Demonstrators set two vehicles ablaze next to the museum and formed a human barricade to block the Mubarak supporters, many of whom retreated onto a nearby bridge, still carrying machetes and rocks.
A day earlier, Tahrir Square, whose name means "liberation," had been the site of the biggest pro-democracy demonstrations in memory here, with hundreds of thousands of people, many of them waving Egyptian flags, gathering for a festive day of songs and chants.
On Wednesday, pro-Mubarak forces waving their own Egyptian flags laid siege to the square, some riding horses and camels, in an attempt to seize the democracy movement's main symbols in an outburst of violence.
Egyptian authorities said that four people died and more than 600 were wounded, but news reports suggested the toll was higher. The Al Arabiya satellite channel reported multiple dead bodies and said one of its reporters was missing. Live television images showed people rushing from the scene with bloodied limbs and skulls, some wounded by chunks of concrete that demonstrators broke loose from a construction site and hurled at the other side.
Vice President Omar Suleiman called on Egyptians late Wednesday to "return to their jobs and their daily lives" because the government had heard the voices of the demonstrators.
In Yemen, President Ali Abdullah Saleh announced that he'll step down in 2013 and drop his drive for constitutional changes that would allow him to be president for life. Saleh, who had come under increased scrutiny after leaked State Department cables quoted him as saying that he'd mislead his public about U.S. drone attacks on Islamic extremists, also promised that his son wouldn't try to succeed him.
The Egyptian crisis has entered an uncertain and dangerous new phase, with Mubarak intent on serving until elections that are scheduled for next fall and activists vowing not to leave the streets until he leaves office. The stakes for both rose sharply in Wednesday's melee, because some activists fear that if they stand down, the regime will target them for reprisals.
"It's an extremely low and disgusting reaction from this dictator, who is willing to put his whole country on fire," said Ahmed Salah, a member of a pro-democracy group called April 6. "This could not happen without the absolute consent of President Mubarak. No one would take this action without him knowing or agreeing."
The group was openly hostile to reporters, with some attacking a CNN camera crew and a young woman in a head scarf trying to force a camera from a McClatchy reporter's hands.
In Washington, State Department spokesman P.J. Crowley said the United States denounced the "violent attacks on peaceful demonstrators and journalists."
Egyptian soldiers let the clashes go on for several hours before they moved to separate the two sides, parking trucks at opposite ends of the square and firing warning shots into the air. By nightfall, soldiers used water cannons to douse fires as both sides continued to square off on roads leading from the square, and the Interior Ministry ordered civilians to evacuate the square.
The military, which had been praised for its refusal to fire on protesters, drew criticism for standing by as the clashes escalated. On Wednesday morning, the army urged demonstrators to stand down in order to restore "normal life to Egypt," an indication to some analysts that the military leadership still backed Mubarak.
Egyptian state television referred to the Mubarak supporters as "pro-stability" demonstrators, but there were signs that they'd been unleashed by the government. Al Jazeera aired images of seized identification cards that identified some as police officers. Many Egyptians regard the police as a cudgel of the regime, and since the first day of the demonstrations the police have been absent from the streets, as if to promote the chaos.
The attacks began after thousands of Mubarak supporters, most of them male and some carrying machetes and sticks, pushed past a thin line of soldiers into the square from various directions, effectively surrounding the demonstrators.
Several dozen angry men then chased a man in a hooded sweatshirt and two young women in jeans and sunglasses out of the square and down a side street in plain view of soldiers. The mob grabbed at the women while others waved their fists and chanted, "Get out!" before the three ducked into a hotel for safety.
"Maintaining security means showing restraint in the use of force, but also in taking appropriate action against those who are using violence," said Heba Fatma Morayef, Egypt researcher at Human Rights Watch. "Restraint does not mean failing to intervene when there are violent attacks against peaceful protesters, or allowing in men on horses or camels."
The Mubarak supporters began laying the groundwork for their siege early Wednesday, hours after the 82-year-old leader gave a televised address saying he wouldn't seek re-election but would use the remainder of his term to set the stage for elections. Some in the crowd appeared moved by the speech, in which Mubarak emphasized his service to the country.
"The turning point was that speech," said Samuel Ibrahim, a 27-year-old Mubarak supporter. "He declared that he will not return to office, and we respect him. Those people," he said, motioning to the pro-democracy group, "they are definitely in the minority."
At daybreak, minibuses and taxis converged on a key bridge leading into Tahrir Square. By noon, small groups of Mubarak supporters marched toward the square, but were held back by Egyptian military tanks on the perimeter.
Around 1 p.m., thousands spilled out of the buses and taxis on the bridge and stormed toward the square. Young men with spray-paint canisters crossed out graffiti that said "Leave" and wrote, "We love you."
A young man in spectacles, whose friend called him Samer but who identified himself as Mohammed Hosni Mubarak _ the president's full name _ said he came because "we love our president." When asked about the democracy protesters, he said, "I want to kill them." In streets just outside downtown, several taxicabs had posters of Mubarak plastered to their back windows. A ragtag group of marchers, mostly women and children wearing plastic flip-flops, chanted pro-Mubarak slogans on the side of the road.
"Poor people. They were obviously paid to do this," said Mohamed Osman, 28, who supports the anti-Mubarak rallies but hasn't joined the protests. "They don't even know they're being used."
(Jonathan S. Landay in Washington and special correspondent Miret El Naggar in Cairo contributed to this article.)
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