Belarus moved police vans and barbed wire into the centre of the capital Minsk on Sunday ahead of a new mass demonstration called for the eve of crunch talks between President Alexander Lukashenko and his main ally, Russia's Vladimir Putin.
Belarusians have been demonstrating against the disputed re-election of Lukashenko for a month, with more than 100,000 people flooding the streets of Minsk for four straight weekends.
Amid an ongoing crackdown on opposition leaders, masked security forces in police vans and military vehicles could be seen preparing in the centre of Minsk ahead of the latest gathering which has been called the "March of Heroes."
On its websites and social media channels, the opposition has announced the slogan "We won't let him sell the country" ahead of Lukashenko's first face-to-face meeting with Putin since protests began, which is set to take place on Monday.
Analysts say Putin may seek to exploit Lukashenko's political vulnerability to wring concessions from him, but any agreements compromising Belarus's sovereignty and independence are likely to enrage Belarusian protesters further.
Over the last week, Lukashenko's security forces have stepped up arrests of opposition figures who are still in Belarus.
After a massive protest last Sunday, Maria Kolesnikova, one of three prominent women opposition figures, was jailed after she resisted expulsion and tore up her passport.
More than 600 people were detained last Sunday in one of the largest waves of arrests since the early days of the demonstrations.
Seeking to intimidate protesters further, men in civilian clothes with batons chased and beat up demonstrators as crowds gradually dispersed last Sunday.
Masked riot police on Saturday violently detained several dozen women demonstrators and threw them into vans during a smaller protest in Minsk.
- 'Heroic people' -
Presidential candidate Svetlana Tikhanovskaya, who the protest movement says won the vote on August 9 but was forced out of the country, paid tribute to all those who planned to take to the streets for Sunday's demonstration, which is set to begin at 1100 GMT.
"Over the past month we have become a truly heroic people," Tikhanovskaya, a political unknown until the election, said in a video address.
"We are continuing our fight for freedom," said the 38-year-old former stay-at-home mother, who has fled into exile in neighbouring EU member Lithuania.
Tikhanovskaya contested the election after her blogger husband was jailed and barred from running along with several other prominent Lukashenko critics.
The unprecedented protests broke out after Lukashenko, who has ruled the ex-Soviet state for 26 years, claimed re-election with 80 percent.
Lukashenko has refused to step down and has turned to Russia for support to remain in power.
On Friday, the United States said it would impose new sanctions on Belarusian figures within days and warned Moscow that continuing to back the strongman would only alienate Belarusians.
Speaking to reporters, US Deputy Secretary of State Stephen Biegun asked how Moscow could "back such a regime and such violence against peaceful citizens."
"If the Kremlin continues down this path, it risks turning the Belarusian people, who have no grievance with Russia, against Moscow," he said.
Historically Russians and Belarusians have enjoyed good relations and the opposition says the protests are not aimed at Russia.
Putin and Lukashenko are set to meet in the Black Sea resort of Sochi on Monday, with the Kremlin saying the talks will cover integration plans as well as key trade and energy projects.
Putin has been keen to unify Russia and Belarus, and Moscow has accompanied its offers of military and economic aid with calls for tighter integration.
Lukashenko has in the past ruled out outright unification with Russia but his options are now limited, analysts say.
His security forces have detained thousands of protesters, many of whom have accused police of beatings and torture.
Several people have died in the crackdown.
UN Secretary General Antonio Guterres said on Friday he was "deeply concerned" over the use of force against peaceful protesters and "the detention of people exercising their legitimate democratic rights."
The European Union said Saturday that it deplored "the increasingly open disregard for the rule of law in Belarus" and reiterated its determination to impose sanctions.
It said it was "ready to take further restrictive measures as necessary."