Egyptian anti-government activists tried to stage a second day of protests around Cairo Wednesday in defiance of an official ban on any gatherings, but police quickly moved in and used tear gas and beatings to disperse the demonstrators.

A day after tens of thousands turned out in several cities for the biggest anti-government protests in years, activists used social networking sites to call for fresh demonstrations. But Facebook, a key tool used to organize protests, appeared to be at least partially blocked in the afternoon.

The Interior Ministry warned police would not tolerate any gatherings, and there was a heavy security presence on the streets, poised to crack down quickly on any new signs of unrest.

Tuesday's demonstrations were the latest in outbursts of political discontent in Egypt that have been growing more frequent and more intense over the past year. Protests have erupted sporadically over police brutality, poverty and food prices, government corruption and mismanagement, and more recently over sectarian strife between Christians and Muslims. Parliamentary elections in November were widely decried as fraudulent.

Many in Egypt see these events as signs of authoritarian President Hosni Mubarak's vulnerability in an election year. There is speculation that 82-year-old Mubarak, who recently experienced serious health problems, may be setting his son Gamal up for hereditary succession. But there is considerable public opposition and, according to leaked U.S. diplomatic memos, it does not meet with the approval of the powerful military. And the regime's tight hold on power has made it virtually impossible for any serious alternative to Mubarak to emerge.

At Wednesday's protests, police fired tear gas to disperse a crowd of several hundred activists on a main commercial thoroughfare in central Cairo, chasing them through side streets as both sides pelted each other with rocks with hundreds of onlookers watching anxiously.

Earlier, dozens gathered outside the Journalists' Union in downtown Cairo and renewed the chants heard against Mubarak throughout Tuesday's much larger protests.

"Mubarak is leaving, leaving. Oh Egyptian people, be brave and join us," they chanted. As police charged the crowd, beating them with sticks, they chanted "peaceful, peaceful."

Many protesters say they have been inspired by the uprising in Tunisia _ even invoking some of the identical slogans heard in the other north African nation.

On Tuesday, protesters clashed with police, who used rubber bullets, water cannons, tear gas and truncheons to disperse them. Three demonstrators and one police officer were killed in the clashes.

The crackdown by Egyptian authorities has brought harsh words from European leaders, who expressed concern and said the events underline the need for democratization and respect for human and civil rights.

However, U.S. Secretary of State Hillary Rodham Clinton did not criticize Egypt's government _ a key U.S. ally in the Middle East _ but only said the country was stable and Egyptians have the right to protest while urging all parties to avoid violence.