Belarusian authorities have detained more than 20 people in the latest wave of arrests, continuing their sweeping crackdown on dissent a year after a disputed presidential election, human rights activists say.

Belarus was rocked by protests which were fuelled by the 9 August 2020 re-election of the authoritarian president, Alexander Lukashenko, to a sixth term in a vote that the opposition and the west rejected as a sham. Lukashenko responded to the demonstrations, the largest of which drew up to 200,000 people, with huge repressions in which more than 35,000 people were arrested and thousands beaten by police.

Belarusian authorities have ramped up the clampdown in recent months, arresting scores of independent journalists, activists and all those deemed not loyal. The Viasna human rights centre said on Thursday that more than 20 people have been detained over the past two days in six cities across the country.

Andrey Dmitriyeu, who was among the challengers to Lukashenko in the presidential vote, was detained for interrogation after a search in his Minsk apartment on Thursday. Dmitriyeu was released later in the day, and it was unclear if he faced any charges.

Ihar Lyashchenya, the former Belarusian ambassador to Slovenia, was arrested on Thursday on charges of “organising mass disturbances”, accusations that carry a prison sentence of up to eight years.

When the post-election protests erupted, Lyashchenya publicly criticised the crackdown on demonstrators and was stripped of his rank by Lukashenko.

Those arrested also include lawyers, political and environmental activists who were part of the Skhod (Assembly) civic initiative intended to encourage a national dialogue.

Stsiapan Latypau, an activist who stabbed himself in the neck with a pen in the courtroom in June in protest against political repressions, faced a hearing on Thursday during which prosecutors asked the court to sentence him to eight-and-a-half years on charges of violation of public order, resistance to the police and fraud.

Latypau, who has been in jail since September, described to the court how police beat him in custody and used a plastic bag to suffocate him.

“I was crying, struggling to breathe in the plastic bag and they just laughed,” he said.

“The masked men beat me with their hands, their feet and using truncheons – they beat me simultaneously and then one by one. They beat me with their fists and palms over my ears, and it felt like a hand grenade exploding inside my head.”

Protests have withered as authorities have moved relentlessly to stamp out any sign of dissent, and opposition leaders have been either jailed or forced to leave the country.

Amid the continuing crackdown, several dozen of women dressed in white and carrying red flowers to represent the colours of the opposition’s red-and-white flag, marched across the Belarusian capital in a silent protest on Thursday.