Investigators in Ukraine's recently liberated southern Kherson region have uncovered 63 bodies with signs of torture after Russian forces left the area.
"We must understand that the search has only just started so many more dungeons and burial places will be uncovered." Denys Monastyrsky, interior minister, told Ukraine's Interfaxnews agency.
Monastyrsky said law enforcement bodies had uncovered 436 instances of war crimes during Russia's occupation.
Eleven places of detention had been discovered, including four where torture had been practiced.
"Investigators are currently examining them and setting down every instance of torture. Exhumations are also taking place of the bodies of those who were killed," Monastyrsky said.
Andriy Kovalenko, a prosecutor in the Kherson regional prosecutor's office, told the New York Times that testimony had been gathered on 800 detentions by Russians in the region.
He said that the most common types of abuse inflicted on detainees were electric shocks, beatings with plastic or rubber nightsticks, and suffocation by pinching the breathing hose on a gas mask placed over a prisoner's head.
Ukrainian and international investigators say what they describe as war crimes have been committed in areas occupied by Russian troops since Moscow's invasion of Ukraine in February.
Russia denies its troops target civilians or have committed atrocities.
Mass burial sites have been found in other parts previously occupied by Russian troops, including some with civilian bodies showing signs of torture.
Russian forces left parts of Kherson region last week -- it had been one of the first areas seized by Russia.
President Volodymyr Zelenskiy, in his nightly video address last Sunday, said investigators had uncovered more than 400 crimes in Kherson.
He said the Russian army left behind corpses, broken infrastructure and landmines in what he described as "the same savagery it did in other regions".