Despite a heavy ban on the opposition, tens of thousands of people have gathered in Belarus to rally by the presidential electoral opponent.
According to Visna, a human rights group, more than 60,000 people demonstrated in the capital Minsk.
The rally was organized by Svetlana Tikhanovskaya, who stands against the long-term president.
Alexander Lukashenko has faced a wave of protests over his bid for a sixth term.
Since Lukashenko took office in 1994, he has extended authoritarian control over Belarus in a style reminiscent of the Soviet era.
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Ms Tikanovskaya, a political novice, decided to stand for the election because her husband was barred from running and going to jail earlier this year.
The AFP news agency said that its supporters had gathered in a section of Minsk to stage the largest opposition in the pre-Soviet country in a decade.
They waved flags and balloons with opposition slogans.
“People who want a decent life are not criminals,” Ms. Tikhanovskaya told the crowd. “They are our people, people who want a peaceful change in power.”
“Please don’t go against your conscience, don’t go against your people,” she said.
State officials have previously accused Ms. Tikankovskaya’s husband, Sergei Tikhanovsky, of associating with Russian businessmen to spark unrest before the election. The popular opposition blogger also faces other charges.
Ms Tikanovskaya denied the allegations, which came during intense action on opposition activity.
Earlier on Thursday, the authorities arrested 33 suspected businessmen, who they accused of plotting “terrorism”. Russia said it was seeking clarification on the arrest and denied the knowledge of the Wagner paramilitary group suspected of involvement in Belarus.
Secretary of the Belarus Security Council, Andrey Ravkov, said investigators suspected that 200 Russian traders had entered the country to “destabilize the situation during the election campaign”.
Mr Ravko said 14 detained people had fought in the Donbas conflict in Ukraine, describing their presence in Belarus as “a very unpleasant situation”.
The United States military and journalists have documented Wagner Group operations in Ukraine, Syria, Libya, Sudan and the Central African Republic, UN investigators report. The Russian government denies any link to the group.
The Belta state news agency Belta has named all 33 Russian suspects and given their date of birth.
Read more about the Wagner Group:
State TV channel Belarus 1 shows Russians arrested in a sanatorium by the Belarus KGB. Video reports (in Russian) said that the group had raised doubts due to their disciplined, military-style behavior – for example they avoided alcohol.
Video footage of the group’s arrest revealed that they had Sudanese currency and a Sudanese phone card. The Wagner Group is known to be active in Sudan, and there is speculation that it was using Belarus as a transit country for African operations.
In Moscow, Kremlin spokesman Dmitry Peskov said on Thursday, “We know that 33 Russians were detained yesterday in Belarus. Two hundred people are still at large. We are not aware of any such illegal activity.” Know which is the basis for his detention. “
He also said that there was no such concept in Russia as “Wagner PMC”.