CAIRO -- Thousands of Egyptians vented their rage against President Hosni Mubarak's autocratic government in a second day of protests Wednesday that defied a ban on public gatherings. Baton-wielding police responded with tear gas and beatings in a crackdown that showed zero tolerance for dissent.

Egypt's largest anti-government protests in years echoed the uprising in Tunisia, threatening to destabilize the leadership of the most important U.S. ally in the Arab world. The ability of the protesters to sustain the momentum for two days in the face of such a heavy-handed police response was a rare feat in this country.

One protester and a policeman were killed Wednesday, bringing the two-day death toll to six. Some 860 people have been rounded up, and Facebook, Twitter and cell phones -- key to organizing protests -- have been disrupted.

Secretary of State Hillary Rodham Clinton called on Egypt to adopt broad reforms and not crack down on the anti-government crowds. She urged the Mubarak regime to "take this opportunity to implement political, economic and social reforms that will answer the legitimate interests of the Egyptian people."

Still, there was no indication that Mubarak, who has ruled with an iron fist for nearly 30 years, intends to relinquish power or make democratic or economic concessions, and no sign he would rein in his security forces.

The defiant demonstrations continued late into the night. In Cairo, dozens of riot police with helmets and shields charged more than 2,000 marchers on a downtown boulevard along the Nile. Smaller clashes broke out across the capital. In one, protesters stoned police, who responded with a volley of tear gas from a bridge over the Nile.

One protester, businessman Said Abdel-Motalib, called the civil unrest "a red light to the regime. This is a warning."

In cities across Egypt, protesters incensed by Egypt's grinding poverty, rising prices and high unemployment hurled rocks and firebombs at police and smashed the windows of military vehicles.

The Interior Ministry warned Wednesday that police would not tolerate any gatherings, and thousands of security forces were out on the streets poised to move quickly against any unrest. Many were plainclothes officers whose leather jackets and casual sweat shirts allowed them to blend in easily with protesters.

Thousands of policemen in riot gear and backed by armored vehicles also took up posts in Cairo, on bridges across the Nile, at major intersections and squares, as well as outside key installations, including the state TV building and the headquarters of Mubarak's ruling National Democratic Party.

Police fired tear gas to disperse a crowd of several hundred activists on a main thoroughfare, chasing them through side streets as both sides pelted each other with rocks while hundreds of onlookers watched. Plainclothes officers shoved some into waiting vans, slapping them in the face.

Observing the clashes, Omima Maher, a 37-year-old housewife lamented her money woes. "Everything is so horrible. I hope we can change it," she said.

A policeman and a demonstrator were killed Wednesday when a car ran them over during a protest in a poor central Cairo neighborhood, security officials said. Earlier, three demonstrators died in clashes in the city of Suez and one policemen was killed in Cairo violence.

In Suez, east of Cairo, a peaceful gathering turned violent at sunset when protesters threw rocks at a morgue where they were waiting for the body of a man killed a day earlier. Police broke up the crowd with tear gas, rubber bullets and live ammunition fired into the air.

Women screamed as they called their sons home, and men vomited in the streets from the acrid white tear gas that filled the air.

Protesters also firebombed the ruling party headquarters and a police station, damaging both buildings as burning trash littered the streets.

In the southern city of Assiut, witnesses said riot police set upon some 100 activists, beating them with batons and arresting nearly half of them. "Down, down Hosni Mubarak!" chanted the crowd. "Oh, people, join us or you will be next."

Although Wednesday's demonstrations were smaller than the tens of thousands who rallied a day earlier, the latest unrest follows repeated public outcries in recent months over police brutality, food prices, corruption and, more recently, sectarian strife between Christians and Muslims.

Parliamentary elections in November were widely decried as fraudulent, rigged to allow candidates from Mubarak's ruling National Democratic Party to win all but a small fraction of the chamber's 318 seats.

Many in Egypt see the events as a sign of the authoritarian leader's vulnerability in an election year. There is speculation the 82-year-old Mubarak, who recently experienced serious health problems, may be setting his son Gamal up for hereditary succession.

There is considerable public opposition to a father-son succession and, according to leaked U.S. diplomatic memos, such a scenario does not meet with the approval of the powerful military. Still, the regime's tight hold on power has made it virtually impossible for any serious alternative to Mubarak to emerge.

Nearly half of Egypt's 80 million people live under or just above the poverty line set by the World Bank at $2 a day. Combined, the poverty, corruption and social disparity pose a threat to Mubarak's regime at a time when he and his son have been unable to improve the lives of the country's poor.

A persistent rumor that Mubarak's family has fled the country was denied Wednesday as "baseless" by a senior ruling party official. However, the fact that such a rumor found legs speaks to the widely held perception that Mubarak could follow the example of Tunisia's longtime authoritarian ruler, who fled the country with his family in the face of that country's popular uprising.

While that is unlikely, failure to rein in the unrest could tempt the military to intervene to take charge of the streets and restore order, or even realign the political order and put forward one if its own as a presidential candidate.

Amr Moussa, the outspoken head of the Arab League once seen as a viable successor to Mubarak, painted a picture of an Arab world that is in turmoil when asked about events in Egypt.

"The Arab citizen is angry, is frustrated. That is the point. So the name of the game is reform," he said at Davos, where he is attending the World Economic Forum meetings.

Many Egyptian protesters say they have been inspired by the uprising in Tunisia -- even invoking the same slogans heard in the north African nation.

German Foreign Minister Guido Westerwelle invoked Tunisia Wednesday, saying the unrest in Egypt "underlines the necessity of democratization, of respect for human and civil rights."

"We are seeing in the last few weeks that a country's stability is not endangered by granting civil rights. It is through the refusal of civil and human rights that societies become unstable," he said.

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Associated Press writers Maggie Michael in Cairo and Hadeel al-Shalchi in Suez contributed to this report.