Clashes broke out at a demonstration aimed at ousting Georgia's Western-backed President Mikheil Saakashvili on Sunday, with protesters attacking cars and police firing rubber bullets and tear gas.

Protesters held an all-night vigil outside the Georgian public television studios in Tbilisi after some 6,000 people rallied on Saturday, accusing Saakashvili of authoritarianism and calling for him to resign.

Police used rubber bullets and tear gas after activists attacked a police car with sticks early Sunday morning, smashing the windows and beating the officers inside, accusing them of trying to kidnap a protest organiser.

"Police were forced to use rubber bullets to defend peaceful citizens," interior ministry spokesman Shota Utiashvili told AFP.

There was a second clash when protesters wielding sticks and improvised shields again attacked cars which they suspected of carrying undercover officers.

Opposition leader Nino Burjanadze, a former parliamentary speaker in the Saakashvili government, said that a "revolution" had started in the ex-Soviet state.

"The authorities' actions have provoked the start of the revolution," Burjanadze told AFP.

Several hundred people continued to protest outside the television studios after the incidents, many of them carrying sticks and some hiding their faces with scarves.

"We want a revolution and we want Saakashvili to step down," protester Mikheil Urchukhishvili told AFP.

Several thousand supporters of the National Assembly opposition alliance rallied in Tbilisi on Saturday, occupying a central square before marching to the public television building.

A parallel protest attended by hundreds of people in the Black Sea resort of Batumi was broken up by police after activists tried to force their way into a local television station, demanding airtime.

The National Assembly alleged that hundreds of its activists have been arrested across the country over the past three days.

"The authorities are carrying out a terror campaign against opposition supporters," Burjanadze said.

But the interior ministry denied this, saying that only 12 people had been detained so far this weekend.

Protesters accuse Saakashvili of failing to tackle widespread poverty and of losing large parts of Georgian territory during the country's disastrous war with Russia in 2008.

But in a sign of the bitter divisions that have split Georgia's opposition, the turnout this weekend was small by local standards as several anti-government parties refused to take part, although some agreed to join the protest on Sunday.

In a televised interview on Saturday night, Interior Minister Vano Merabishvili said that the low turnout proved that there was no public support for radical opposition actions.

"These people are so few, so weak that they cannot do anything," he said.

Saakashvili's pro-Western administration -- which deployed riot squads to crush demonstrations in 2007 at a time when Burjanadze was a leading official -- has said it supports the right to peaceful protest.

Despite defeat in the war with Russia and the crackdown in 2007, Saakashvili has remained the country's most powerful figure and many believe he could continue to dominate Georgian politics after his term ends in 2013.