Sources including human rights groups have told Euronews that at least 283 people were detained by police as anti-government protests continued across Belarus on Sunday.
Demonstrations have now been going on for 16 consecutive weeks, attracting thousands of people, calling for president Alexander Lukashenko to resign.
Security forces have habitually used stun grenades, tear gas and mass arrests in attempts to deter the protests.
There have been near-daily protests since early August, but those on Sundays have been the largest, particularly in the capital Minsk.
The rallies started after the presidential election on August 9 that gave a sixth term in office to Alexander Lukashenko, according to official results.
But the opposition and some poll workers say votes were manipulated and protesters are calling on the president to step down.
On Sunday demonstrators tried to dilute detentions and dispersals by initially gathering in various parts of the capital Minsk, but they were met by police when they tried to converge to the centre.