Belarusian opposition leader Svetlana Tikhanovskaya has called for nationwide strike action to go ahead on Monday after police fired stun grenades at crowds marching against the president.
Ms Tikhanovskaya issued an ultimatum earlier this month threatening action if Alexander Lukashenko did not resign.
Protests have swept the country since Mr Lukashenko claimed victory in an August poll widely viewed as rigged.
Human rights group Vesna said that more than 150 people had been detained.
“Today the regime has once again shown Belarusians that violence is the only thing it is capable of,” Ms Tikhanovskaya said in a social media post, adding: “Therefore tomorrow, October 26, a national strike will begin.”
Earlier, tens of thousands of demonstrators marched for the 11th successive Sunday of protests.
Footage showed people running from flashes and loud bangs as they tried to make their way to Mr Lukashenko’s residence at the Independence Palace in the capital, Minsk.
Ms Tikhanovskaya issued her ultimatum on 13 October, threatening a mass walkout by workers if Mr Lukashenko – who has ruled Belarus for 26 years – ignored their demands.
On Sunday, protesters gathered in the streets of Minsk and other cities across Belarus, many waving the opposition’s red and white flags and chanting “strike” as they marched.
Local media estimated that about 100,000 people had joined the demonstration in the capital.
The country’s interior ministry told Russia’s Tass news agency that riot control weapons had been deployed as darkness fell and large crowds continued to make their way through the streets of the capital.
According to other Russian news agencies, citing their correspondents at the scene, at least 10 devices had gone off. There have also been reports that riot police fired rubber bullets.
Security forces also blocked roads in central Minsk and water canon were put in place.
Videos posted on social media earlier showed buses transporting security personnel to central Minsk.
Ms Tikhanovskaya had earlier this month called for a nationwide strike because Belarus had “had enough” after two months of “political crisis, violence and lawlessness”.
She issued three demands from a location in Lithuania, where she has been in exile since August.
The ultimatum is an attempt to increase the political pressure on Mr Lukashenko but it also seems intended to inject new energy into the street protests.