More than 1,000 protesters chanting "Shame!" and "Long live Belarus!" defied a ban and confronted police on Saturday as they tried to stage a rally in Minsk against President Alexander Lukashenko's re-election.
Riot police, clad in black and equipped with batons, drafted in reinforcements to handle crowds who surged out of side streets towards Minsk's central October Square.
Some scuffling ensued as some demonstrators pushed their way through a police cordon. But police generally prevented the protesters from getting onto the square, site of a tent camp cleared away by police on Friday.
Defeated opposition candidate Alexander Milinkevich told protesters to go to the nearby Yanka Kupala park to continue their rally.
In line with the pattern earlier in the week, police showed tolerance unusual for the tightly-controlled ex-Soviet state and refrained from using force to break up the demonstration.
Earlier Milinkevich, credited with only 6 percent of the vote to Lukashenko's 83 in the March 19 election, had urged supporters to mass "no matter what" in October Square.
The rally was also billed as a commemoration of the independence day of a short-lived Belarussian republic in 1918.
The five days of protests against an election that the opposition says was blatantly rigged are unusual in Belarus, where dissent is normally nipped in the bud by Lukashenko's state security service.
Numbers at previous demonstrations this week have varied from several thousand last Sunday night to the 200 or so who were rounded up by police early on Friday morning.
Demonstrators are demanding a re-run of the poll, which handed Lukashenko five more years in power.
Events in Belarus have set Russia, which endorses Lukashenko's election victory, at odds with the United States and Western Europe.
The United States and European Union issued separate statements denouncing the police action and announcing plans to impose restrictions, including a travel ban on Belarussian officials in the aftermath of the election.
According to incomplete opposition figures, police detained more than 260 demonstrators in the square and drove them off in trucks to a pre-trial detention centre.
Opposition supporters said riot police had pulled Alexander Kozulin out of a crowd of protesters marching on a detention centre where about 200 of their comrades are being held.
Separately, Interfax news agency reported that Alexander Milinkevich, the main leader of the opposition, had also been detained but an aide denied the report.