Police in Belarus detained 345 people at nationwide anti-government protests on Sunday, the Interior Ministry said in a statement.
Thousands took to the streets of the Belarusian capital Minsk on Sunday, with police using stun grenades to disperse the crowd.
Opponents of President Alexander Lukashenko have staged regular protests since August, accusing him of rigging the election to extend his 26-year grip on power.
He denies electoral fraud and has refused to resign, Reuters reported.
Protest organizers this week asked people to gather in dozens of different spots all across Minsk before forming bigger groups, to make it more difficult for police to control the crowd.
The street rallies were re-ignited following the death of a 31-year old anti-government protester Roman Bondarenko, who died in hospital earlier this month following what demonstrators said was a severe beating by security forces.
The interior ministry denied responsibility for Bondarenko's death, saying he was killed in a scuffle with civilians.