Egyptian security officials say police have put Nobel Peace laureate Mohamed ElBaradei under house arrest. Police stationed outside his suburban Cairo home told him he cannot leave the house after he joined tens of thousands of protesters in the capital Friday.

ElBaradei returned to the country Thursday night from a month abroad and declared he was ready to lead the protesters to a regime change.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

CAIRO (AP) _ Tens of thousands of anti-government protesters poured into the streets of Egypt Friday, stoning and confronting police who fired back with rubber bullets and tear gas in the most violent and chaotic scenes yet in the challenge to President Hosni Mubarak's 30-year rule. Even a Nobel Peace laureate was soaked by water cannon and forced to take refuge in a mosque.

Groups of thousands of protesters, some chanting "Out! Out! Out!" gathered at at least six venues in Cairo, a city of about 18 million people. Many marched toward major squares and across Nile bridges, setting off clashes with police. Security officials said there were protests in at least 11 of the country's 28 provinces.

It was a major escalation of protests that began on Tuesday to demand Mubarak's ouster and vent rage at years of government neglect of rampant poverty, unemployment and rising food prices. Security officials said protesters ransacked the headquarters of Mubarak's ruling party in the cities of Mansoura north of Cairo and Suez, east of the capital.

Internet and cell phone services were cut off early Friday in Cairo and remained down in an extreme but inadequate attempt to stop protesters organizing. Facebook, Twitter and Blackberry Messenger also saw interruptions.

"It's time for this government to change," said Amal Ahmed, a 22-year-old protester. "I want a better future for me and my family when I get married."

The protesters say they were emboldened by the uprising in Tunisia, another North African Arab nation. Egypt, Washington's closest Arab ally, may be losing U.S. support. The Obama administration has publicly counseled Mubarak, 82, to introduce reforms and refrain from using violence against the protesters.

Police fired water cannons at one of the country's leading pro-democracy advocates, Nobel Peace laureate Mohamed ElBaradei, and his supporters as they protested after noon prayers. They used batons to beat some of ElBaradei's supporters, who surrounded him to protect him.

A soaking wet ElBaradei was trapped inside a mosque while hundreds of riot police laid siege to it, firing tear gas in the streets around so no one could leave. Tear gas canisters set several cars ablaze outside the mosque and several people fainted and suffered burns.

"We are the ones who will bring change," said 21-year-old Ahmed Sharif, one of scores who were with ElBardei. "If we do nothing, things will get worse. Change must come!" he screamed through a surgical mask he wore against the tear gas.

Police allowed thousands of protesters to march to one bridge across the Nile, where officers stopped and formed lines to halt their progress. Ferocious fighting ensued, with demonstrators hurling rocks and tear-gas canisters at police.

Several marchers fell with what appeared to be sprays of small buckshot wounds, and protesters were carrying others, bleeding and unconscious, into cars that hurried them to hospitals. An apartment block caught fire _ it was unclear if the cause was arson or an accident set off by a hot tear-gas canister.

Protesters and police waged similar skirmishes at Ramsis and Tahrir squares in the heart of the city.

Television footage showed protesters were throwing rocks onto police from a highway overpass near Tahrir Square, while a police vehicle sped through the crowd spraying tear gas on demonstrators.

In the upscale Mohandiseen neighborhood, a crowd that doubled to about 20,000 marched toward the city center chanting "Down, down with Mubarak!"

Residents waved and whistled in support from apartment windows, some waving the red, white and black Egyptian flags.

In downtown Cairo, people on balconies tried to help protests cut the sting of the tear gas by tossing cans of Pepsi and bottles of water to douse their eyes, and onions and lemons to sniff.

Abeer Ahmed, a 31-year-old woman who showed up to see ElBaradei with her toddler, said she has a law degree but makes a living cleaning homes.

"Nothing good is left in the country," she said. "Oppression is growing."

The troubles were preventing trains from coming to Cairo, with their last stop now before reaching the city are south and north of the capital, security officials.

Mubarak has not been seen publicly or heard from since the protests began Tuesday. He and his government have shown no hint of concessions to the protesters who want political reform and a solution to rampant poverty, unemployment and rising food prices.

While he may still have a chance to ride out this latest challenge, his choices are limited, and all are likely to lead to a loosening of his grip on power.

The president has not said yet whether he will stand for another six-year term as president in elections this year. He has never appointed a deputy and is thought to be grooming his son Gamal to succeed him despite popular opposition. According to leaked U.S. memos, hereditary succession also does not meet with the approval of the powerful military.

Continuing the heavy-handed methods used by the security forces the past three days would probably buy the Mubarak regime a little time but could strengthen the resolve of the protesters and win them popular sympathy.

The alternative is to introduce a package of political and economic reforms that would end his party's monopoly on power and ensure that the economic liberalization policies engineered by his son and heir apparent Gamal over the past decade benefit the country's poor majority.

He could also lift the emergency laws in force since 1981, loosen restrictions on the formation of political parties and publicly state whether he will stand for another six-year term in elections this year.

Friday's demonstrations were energized by the return of ElBaradei on Thursday night, when he said he was ready to lead the opposition toward a regime change.

They also got a boost from the endorsement of the country's biggest opposition group, the Islamic fundamentalist Muslim Brotherhood. The group called its supporters to join the protests on Friday.

The Brotherhood, outlawed since 1954, is Egypt's largest and best organized opposition group. It seeks to establish an Islamic state. It renounced violence in the 1970s and has since been a peaceful movement. Its network of social and medical services has traditionally won it popular support, but its detractors say its involvement in politics has chipped away at its support base.

It made a surprisingly strong showing in 2005 parliamentary elections, winning 20 percent of the legislature's seats, but it failed to win a single seat in the latest election late last year. The vote is widely thought to have been marred, rigged to ensure that Mubarak's ruling party win all but a small fraction of the chamber's 518 seats.

Egypt's four primary Internet providers _ Link Egypt, Vodafone/Raya, Telecom Egypt, Etisalat Misr _ all stopped moving data in and out of the country at 12:34 a.m., according to a network security firm monitoring the traffic. Telecom experts said Egyptian authorities could have engineered the unprecedented cutoff with a simple change to the instructions for the companies' networking equipment.

The Internet appeared to remain cut off in Cairo but was restored in some smaller cities Friday morning. Cell-phone text and Blackberry Messenger services were all cut or operating sporadically in what appeared to be a move by authorities to disrupt the organization of demonstrations.

Egyptians outside the country were posting updates on Twitter after getting information in voice calls from people inside the country. Many urged their friends to keep up the flow of information over the phones.

A Facebook page run by protesters listed their demands. They want Mubarak to declare that neither he nor his son will stand for next presidential elections; dissolve the parliament holds new elections; end to emergency laws giving police extensive powers of arrest and detention; release all prisoners including protesters and those who have been in jail for years without charge or trial; and immediately fire the interior minister.

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Associated Press reporter Hadeel Al-Shalchi contributed to this report from Cairo.