At least 100 people have been arrested in the Belarusian capital Minsk and other towns as protests against President Alexander Lukashenko were held for a fourth weekend in a row.
In Minsk, police charged demonstrators near the presidential palace, firing pepper spray and wielding batons.
Tens of thousands of people defied heavy security and rallied in the city.
Demonstrators want the long-time president to resign after his re-election last month amid allegations of ballot-rigging.
Mass unrest since then has seen at least four people killed and hundreds injured as the government tries to stamp out dissent.
A number of opposition figures have fled Belarus.
On September 5, activist Olga Kovalkova became the latest to say she had taken refuge in neighboring Poland amid threats of imprisonment.
President Lukashenko, in power since 1994, has accused Western nations of interfering.
Protesters, human rights activists and observers say riot police are brutally suppressing peaceful marches in the former Soviet republic.
Belarus borders Russia, on which it depends heavily for energy and with which it historically has close ties, as well as Ukraine and EU states.
After the Viasna non-governmental organization reported 130 arrests on September 6, the Belarusian interior ministry confirmed for Russian news agency Interfax at least 100 detentions across the republic.
Eyewitnesses told Interfax that police began to make arrests in Minsk after the unsanctioned rally ended and people were going home. Video footage on September 7 shows men in plain clothes beating peaceful protesters with batons.
Internal Affairs Minister Yuri Karayev defended the actions of the security forces.
“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,” he was quoted as saying by the official Belta news agency.
September 6 has become the key day for street demonstrations since the rallies began.
In recent days the security forces – dressed all in black with balaclavas over their faces – targeted university students as they returned from their holidays, dragging some from the streets and university buildings into unmarked minivans.
Protests have also been reported in other Belarusian cities and towns including Mogilev, Grodno, and Gomel.