Belarus Police arrested 100’s of people protesting against President Alexander Lukashenko in capital Minsk and other towns.
Tens of thousands of people took part in the march even though police issued warnings.
Riot police used pepper spray and wielded batons against demonstrators near the presidential palace.
Protesters demand end of Lukashenko’s 26-year rule after he was re-elected last month amid mass allegations of ballot rigging.
The unrest has entered the fourth week. At least four people were killed and hundreds injured in numerous clashes between police and commoners.
Human rights activists have say riot police are brutally suppressing peaceful marches.
President Alexander Lukashenko’s government has defended police action. “They talk about the brutality of the Belarusian police, and I want to say this: there are no more humane, restrained and cool-headed police anywhere in the world,” Internal Affairs Minister Yuri Karayev was quoted.
Opposition leader, Svetlana Tikhanovskaya, who has sought refuge in Lithuania, urged the UN to help halt the authorities’ crackdown on protesters.
Last month, EU leaders agreed to impose sanctions – including asset freezes – on as yet unnamed Belarusian officials involved in alleged election-rigging, brutality and imprisonment of protesters.
The UN special rapporteur on Belarus, Anais Marin, said Mr Lukashenko’s re-election as president was “completely manipulated” and “people’s votes were stolen”.
President Lukashenko has denied any allegations of vote-rigging. He has blamed some EU nations, in particular Poland and Lithuania, of trying to force regime change.