Meanwhile, Air France cancelled more flights to Moscow after Russian authorities failed to approve flight plans that avoid Belarus airspace.
Tens of thousands of demonstrators organised at least 100 separate gatherings in the capital Minsk.
Police detain dozens of people during protests against President Alexandre Lukashenko's contested re-election, activists say.
More than 700 people taken into pre-trial detention for "breaching the laws on mass gatherings," Interior Ministry says.
Belarusian students, factory workers and pensioners answered a call by exiled opposition figure Svetlana Tikhanovskaya to launch a nationwide strike this week — a fresh move to force Lukashenko to hold new elections after months of mass protests.
Belarus' Sviatlana Tsikhanouskaya says a national strike will begin Monday after President Alexander Lukashenko's government responded with force to protests against him.
Belarus has been rocked by strikes and weekly street protests since authorities announced that President Lukashenko, who has ruled in authoritarian fashion since 1994, had secured re-election on August 9 with 80 percent of votes.
Protesters have taken to the streets every week since an August vote to demand that President Lukashenko step down and allow for a new election to be held.
President Alexander Lukashenko holds a rare meeting with detained opposition leaders, state-run Belta news agency reports.
Belarusian opposition leader Svetlana Tikhanovskaya faces a charge in Belarus over making public calls to harm the country's security.
Top opposition Telegram channel, Nexta, says authorities have opened more than 250 criminal cases against President Lukashenko's would-be rivals, activists, bloggers, and ordinary Belarusians.
Protest leader Maria Kolesnikova is not in police custody, officials confirm after reports that she had been forcefully taken by unidentified people in central Minsk.
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