Police armed with nightsticks, shields and assault rifles swept opposition supporters off a central bridge across the Sava at around midnight, ending a four-hour standoff. One of the leaders of the pro-democracy movement, Vesna Pesic, was beaten by police.
Witnesses at the eastern end of the bridge said police used water cannon against demonstrators for the first time since the opposition began marching to demand the regime respect their victory in local elections on 17 November.
Zoran Djindjic, head of the Democratic Party, said Ms Pesic was beaten on her feet, hands and ribs and was fearing arrest.
The streets leading from the bridge towards Republic Square were littered with postersdropped by protesters, while police at the eastern end extinguished fires lit to keep demonstrators warm during the icy wait. One medical worker said at least 10 people had been hurt. At least 1,000 riot police were visible in the city, aided by four water cannon parked near Republic Square.
Within 30 minutes of the first charge, several hundred demonstrators had gathered in the square where the opposition rallies meet each night and were hurling insults at dozens of policemen massed in lines along a main road. The crowd screamed "fascists, fascists" and blew whistles. The police, who appeared stony-faced and unfriendly compared to earlier days, began to move, batons raised, against the crowd, which scattered across the square.
Vuk Draskovic, the third leader of the Zajedno (Together) opposition alliance, said he was chased by plainclothes police as he fled and said shots were fired at his car. Speaking on the city's independent radio, he said the brutal police action "in effect" represented "a state of emergency". During clashes passers-by received whacks from police batons. The police, reinforced in several waves, cleared the square and the main streets and then stood, holding their ground inside the opposition heartland.
It is not clear why the police should have blocked a route used frequently by the opposition on its marches, nor why they should then have attacked the remaining demonstrators in the square.