A top Ukrainian human rights investigator on Thursday released a video of what he said was a torture chamber used by Russian forces in the recently liberated Kherson region, including a small room in which he said up to 25 people were kept at a time.

Dmytro Lubinets, the parliament's human rights commissioner, shared the video on social media after Ukraine's interior minister said investigators had uncovered 63 bodies with signs of torture after Russian forces left last week.

In the video, Lubinets speaks from a series of bare underground rooms -- with grimy walls and floors -- that he says were used for detentions, interrogations and torture. Electric shocks were used to secure confessions, he said.

Reuters was unable to verify the allegations made by Lubinets and others in the video. Russia denies its troops target civilians or have committed atrocities.

An unidentified middle-aged man in the video said he had been kept in one of the rooms for 24 days. He said he was tied to a chair and subjected to recurring electric shocks "until losing consciousness" and, after a break, the process resumed.

"They asked the questions they wanted and obtained the answers they wanted," the man said. "One after the other. They prepared a bunch of questions and wrote down everything they wanted."

The premises, Lubinets said, were clearly not built for accommodating large numbers of people.

"You can see that people who were detained here were simply not allowed to go to the toilet," Lubinets said in the video, posted on the Telegram messaging app and Facebook.

Earlier on Thursday, according to Ukrainian media, Interior Minister Denys Monastyrsky said on national television that 63 bodies with signs of torture had been discovered by investigators in the Kherson region, adding that "we must understand that the search has only just started so many more dungeons and burial places will be uncovered."

Monastyrsky said law enforcement had uncovered 436 instances of war crimes during Russia's occupation of Kherson, which began shortly after the February invasion of Ukraine by Russian forces and ended last week. Eleven places of detention had been discovered, including four where torture had been practiced, he said.

A police station known as 'The Hole' was the most notorious of several sites where, according to more than half a dozen locals Reuters spoke to in Kherson city, people were interrogated and tortured during Russia's nine-month occupation.

Mass burial sites have been found in other parts previously occupied by Russian troops, including some with civilian bodies showing signs of torture.