Russia demanded an explanation from Belarus on Thursday, after Minsk arrested a group of alleged Russian mercenaries and said they were suspected of plotting "acts of terrorism" before a presidential election.
Belarusian state television broadcast footage on Wednesday of more than 30 suspected Russian private military contractors being detained near the capital Minsk. Authorities said they had received information that over 200 fighters had entered the country to destabilise it before the Aug. 9 election.
A criminal case was opened on Thursday after Belarus said is suspected "the preparation of terrorist acts". Some of the captured men had confessed to trying to orchestrate a revolution, and Russia's ambassador was summoned to explain, officials said.
Tensions over the arrests risk worsening already strained relations with traditional ally Russia.
Moscow denies it uses mercenaries. Kremlin spokesman Dmitry Peskov said Moscow wanted an exhaustive explanation from Belarus about the group detained and hoped their rights would be observed fully.
"We don't have information about any illegal activity carried out by them," Peskov said in Moscow. "We hope to receive information that will allow us to sort this out".
The election campaign that has posed the biggest challenge in years to Belarusian President Alexander Lukashenko, who has allowed little dissent in over a quarter of a century in power in the country of 9.5 million between Russia and European member state Poland.
Authorities announced additional security measures for campaign events on Thursday. The opposition feared Lukashenko would use the alleged plot to intensify a crackdown on rivals.
Lukashenko, 65, has accused opponents of working with foreign backers to overthrow him and has jailed two of his main election rivals.
He is expected to win the election despite growing opposition and concerns about the economy, human rights and his handling of the COVID-19 pandemic.
'PLOTTING A REVOLUTION'
Belarusian Security Council State Secretary Andrei Ravkov told reporters up to 200 mercenaries were being hunted by law enforcement agents.
Andrey Dmitriev, a presidential candidate, quoted Ravkov as saying some of the people detained had confessed to plotting "a revolution".
They were alleged to have trained in the Russian cities of Pskov and Nevel and were mostly bombers and snipers, Dmitriev told reporters after meeting Ravkov. The authorities did not rule out shutting down internet access in Belarus, he said.
State media have suggested the detained men worked for Wagner, a private military contractor.
Footage of the group's arrest showed they had Sudanese currency and a Sudanese phone card with them, prompting some Belarusians to suggest they were going through Minsk en route to Africa.
Responding to criticism, Lukashenko says he has delivered years of economic and political stability and that the state covers many of people's core needs as in Soviet times.
After weeks of street protests, the opposition has rallied around Svetlana Tikhanouskaya, the wife of one of the jailed election candidates, who took his place after his arrest.