The Belarusian human rights group Viasna says more than 300 people were arrested and many of them beaten by police during protests calling for the country’s authoritarian president to resign.
The demonstrations, which attracted thousands, were the 16th in a row on Sunday of large-scale protests against President Alexander Lukashenko.
There have been almost daily protests since the beginning of August, but those on Sundays have been the largest.
Protests have gripped Belarus since the August 9 presidential election, which reportedly gave Lukashenko a sixth term, but the opposition and some pollsters say they were manipulated.
Throughout the wave of protests, more than 19,000 people have been detained and thousands beaten, human rights advocates say.
On Sunday, protesters tried to dilute arrests and police dispersals by initially gathering in different parts of the capital Minsk, but were met by police as they tried to converge in the city center. Police used stun grenades to turn them around and began capturing large-scale prisoners.
Protests also took place in other cities on Sunday. Viasna said at least 304 people were arrested across the country.