The Belarusian human rights group Viasna has said more than 140 people have been arrested and many of them beaten by police during protests calling for the country’s president to resign.
The demonstrations that attracted thousands were the 16th consecutive Sunday of large protests against President Alexander Lukashenko.
There have been near-daily protests since early August but those on Sundays have been the largest.
Protests have gripped Belarus since the August 9 presidential election that gave Mr Lukashenko a sixth term in office.
The opposition and some poll workers claim the results were manipulated.
Throughout the protest wave, more than 19,000 people have been detained and thousands of them beaten, human rights advocates say.
The protesters on Sunday tried to dilute detentions and police dispersals by initially gathering in various parts of the capital Minsk but were met by police when they tried to converge on the city centre.
Police used stun grenades to turn them back and began large-scale detentions.
