Georgian security forces fired tear gas and water cannons into a crowd of hundreds of anti-government protesters on Wednesday, driving them from a central street in front of parliament and beating several with truncheons.

The daily demonstrations in the capital over the past week are part of the worst political crisis that President Mikhail Saakashvili -- a staunch U.S. ally -- has faced since he was propelled to power in the 2003 Rose Revolution mass protests.

Helmeted riot police with shields advanced toward the crowd on Wednesday as demonstrators retreated down Tbilisi's main avenue in the face of the assault. Several hundred officers swept down the street in front of the building, where opponents of Saakashvili have protested since Friday.

Police fired tear gas from the beds of pickup trucks. Many wore gas masks, and live television broadcasts showed several people choking, including police. Scattered fistfights broke out between uniformed police and protesters.

Paramedics treated victims as ambulances stood nearby, and several civilians lay on the ground as people poured water into their eyes and a cloud of gas drifted through the streets. Cordons of police blocked off side streets.

The protests have drawn thousands of people to the parliament building to demand Saakashvili's resignation and call for changes in election schedules and legislation.

In the early morning, police forced dozens of demonstrators from the site where they had remained overnight, and detained two opposition leaders. But demonstrators streamed back a few hours later and the crowd grew to more than 1,000 people. Police wielded truncheons as they sought to keep protesters off the main street, and beat several people.

More than 50,000 people rallied at the start of the protests on Friday. The initial demand was for changes in the dates of planned elections and in the electoral system, but later the central demand became Saakashvili's resignation.

The protests are centered at the same site as the 2003 Rose Revolution demonstrations, which led to the resignation of longtime leader Eduard Shevardnadze and ushered Saakashvili into power.

Many of the pro-Western president's opponents support his aims, such as closer ties with the United States and Europe.

But opponents accuse Saakashvili of sidestepping the rule of law and sliding toward authoritarianism, creating a system marked by violations of property rights, a muzzled media and political arrests.