Belarus on Tuesday detained at least 24 people, including recently freed political prisoners, Minsk's leading rights group said, warning families of regime critics to be vigilant.
Ruled by President Alexander Lukashenko since 1994, Belarus has for almost four years brutally cracked down on anyone who took part in massive anti-regime protests in 2020.
"There are arrests all over the country," Viasna, a rights group that monitors arrests, said on its website.
"Among them are former political prisoners that have been freed but stayed in Belarus," it added.
Hundreds of thousands fled Belarus, mainly to neighbouring Poland but also to Lithuania, since the mass 2020 protests.
Belarus, whose security service is still called the KGB as it was in the Soviet-era, has gone after the remaining pockets of dissent still inside the country.
"KGB employees are en masse going to the relatives of political prisoners and former political prisoners," Viasna warned.
It called on the families of those who have denounced the regime to "look out for their safety."
Viasna -- founded by jailed Nobel Prize-winning activist Ales Bialiatski -- says there are 1,415 political prisoners in Belarus.
The arrests came ahead of a planned meeting between Lukashenko and his Russian counterpart Vladimir Putin this week.
The country's exiled opposition leader, Svetlana Tikhanovskaya, warned of "another wave of searches and mass detentions in Belarus."
"The regime's thugs have targeted former political prisoners and the families of those currently held," she said in a post on Twitter.
Protests erupted in Belarus in 2020 after Lukashenko was accused of rigging an election, which the opposition say was actually won by Tikhanovskaya.
She later fled the country after the regime brutally suppressed the protests.
Her ally -- Maria Kolesnikova -- chose to stay in Belarus, and tore up her passport during a forced deportation attempt.
She is serving an 11-year sentence and her health is believed to have seriously degraded in prison.
Isolated for years, Belarus has become even more secluded since Lukashenko allowed Moscow to use Belarusian territory to launch its Ukraine offensive.