According to Viasna, the musician had blocked traffic by waving a red and white flag and encouraged demonstrators to clap their hands.
ADVERTISEMENTBelarus has sentenced a drummer to six years in prison for playing during opposition demonstrations, human rights activists have said.
Alexei Santchuk was arrested in Minsk last November along with other members of his band, who often performed at anti-government marches.
They were initially sentenced to 15 days in prison for participating in "unauthorised demonstrations" against the re-election of President Alexander Lukashenko.
But on Thursday, a Belarusian court found Santchuk guilty of more serious offenses, the human rights NGO Viasna said in a statement.
The drummer was convicted of "seriously violating public order" and inciting people to participate in "mass riots", they added.
According to Viasna, Santchuk was accused of blocking traffic by waving a red and white flag - the colours of the Belarus opposition - and of encouraging demonstrators to clap their hands.
"The musician was reportedly beaten after arrest and reported pressure while speaking in court," Viasna said, claiming that he was then forced to record a videotaped confession on state television.
Belarus' opposition has long disputed the re-election of Lukashenko in the August 2020 presidential election.
For several months, thousands of citizens have taken part in mass protests across the country, amid a brutal crackdown by the authorities. Most senior opposition figures have been imprisoned in Belarus or were forced into exile, including former presidential candidate Sviatlana Tsikhanouskaya.