The protest at the “hero city” monument honouring Minsk’s suffering and resilience during the Second World War attracted at least 100,000 people, according to a messaging app channel used by the opposition.
Police said 125 people were arrested, but Ales Bilyatsky of the Viasna human rights organisation said that more than 200 were detained.
Wide protests began after the August 9 presidential election that officials say gave President Alexander Lukashenko a landslide 80% win over his main challenger, Sviatlana Tsikhanouskaya, a former teacher and the wife of a popular jailed blogger.
Mr Lukashenko, who has been in office since 1994, has been defiant but beleaguered, unable to put down the largest, most sustained wave of protests yet in this Eastern European nation of 9.5 million people.
He has refused to rerun the election, which both the European Union and the United States have said was not free or fair, and refused offers from Baltic nations to help mediate the situation.
Mr Lukashenko says he has reached an agreement with Russian President Vladimir Putin that Russia will send in security help if asked. But Russia has appeared hesitant to get involved deeply in the Belarus unrest.
Mr Putin and Mr Lukashenko talked by phone on Sunday, but a Kremlin statement gave few details of the conversation, other than noting that Mr Putin had congratulated the Belarusian leader on his 66th birthday.
Ms Tsikhanouskaya, who fled to Lithuania after the election because of concerns about her security, gave a withering acknowledgement of the birthday.
Speaking by telephone from the Lithuanian capital of Vilnius, she said: “I wish him to overcome his fears, look truth in the eye, listen to the voice of the people and go away.”
Mr Lukashenko has consistently blamed Western countries for encouraging the protests, and contends that Nato is repositioning forces along Belarus’ western border with the aim of intervening in the unrest – a claim the alliance strongly denies.
The Belarusian Defence Ministry said on Sunday that it was conducting military exercises in the Grodno region, near the borders of Poland and Lithuania, simulating defending against an invasion.
