Protesters in Belarus faced repression on Sunday, as security forces reportedly fired warning shots to stop demonstrators from gathering.

It was the 13th Sunday in a row that anti-government protesters gathered since Belarusian President Alexander Lukashenko won a contested election.

The opposition has rejected the outcome as fraudulent and considers its leader, Sviatlana Tsikhanouskaya, to be the actual winner of the vote.

Belarusian newspaper Nasha Niva reported that tens of thousands of people swept through the capital, Minsk, in Sunday's protest, while Human rights group Visana put the figure at 20,000.

Photo and video footage shared on the messaging app Telegram showed streets lined with uniformed people in riot gear facing protesters. Visana said more than 240 detentions took place, including of journalists on the scene.

The independent news portal tut.by published photos showing off-road vehicles with machine guns on the roof in Minsk.

Read more: Belarus threatens to use firearms against protesters

"The situation is really alarming and everyone's mood is tense," one protester who requested anonymity told Reuters via phone.

"Police buses and equipment are constantly driving past the column. It feels like people are ready for any kind of escalation," the protester said.

Large crowds reportedly gathered in eastern Minsk and headed toward Kurapaty, a wooded area on the outskirts of the capital, where over 200,000 people were executed during Stalinist-era purges.

Protesters carried banners with slogans such as "The people's memory (lasts) longer than a life of a dictatorship'' and "Stop torturing your people!'' connecting Stalin's brutal era with life under Lukashenko.

Lukashenko: 'We will not back down'

Ahead of the march, security forces had already cordoned off several central squares, closed several metro stations and in some cases, mobile internet disruption was reported.

Belarusian President Alexander Lukashenko signaled that he was ready to crack down on demonstrators. "It's enough now. We will not back down," Lukashenko said on Friday.

"If someone touches a member of the military, they must leave at least without their hands," he added in a sign of support to security forces.

Read more: Belarusians are taking their children to anti-Lukashenko protests

Last week, Lukashenko also partially closed the border to the west and replaced his interior minister.

The opposition responded by naming Sunday's protest the "March against terror" while organizers said of Lukashenko: "He has declared war on his own people."

jcg, jsi/rc (AFP, Reuters, AP)