The United Nations' special rapporteur to Belarus likened the country to a totalitarian regime Sunday.
Anais Marin urged authorities to release over 500 people whom right groups consider political prisoners.
Marin cited the case of jailed journalist Raman Pratasevich, whose Ryanair flight from Greece to Lithuania in May had been diverted to land in Minsk, where he was immediately arrested.
Speaking to the Human Rights Council in Geneva, Switzerland, Marin said the incident "illustrates the desire of authorities to end all forms of dissidence by purging society of elements it considers undesirable."
"It is a form of purge that recalls those practiced by totalitarian states," she went on.
In August, protests broke out over a controversial election in which longtime leader Alexander Lukashenko declared victory.
More than 35,000 people have been jailed since Lukashenko's election, with opposition candidates either in hiding outside the country or in jail, according to the U.N.
Many countries' representatives at the council also denounced Belarus' human rights abuses, with the United States hinting at more sanctions.
"Such contempt for international norms cannot go unanswered," Benjamin Moeling, the U.S. delegate, said, adding that the U.S. "will consider further actions as necessary."
The U.S. has enacted multiple rounds of sanctions against Belarus, including as recently as two weeks ago.
European Union foreign ministers also announced late last month a fresh raft of sanctions against the Belarusian government, this time targeting 86 officials and state-owned entities, closely following Pratasevich's arrest.
So far, Western sanctions imposed on Belarus have had little effect in persuading Lukashenko to pull back from his crackdown on dissent. Belarusian authorities have detained and tortured thousands of protesters, according to rights groups.
Some information for this report came from Reuters.