(CNN)Researchers at Yale University say they have uncovered 21 "filtration" sites in the Russian-controlled territory of Donetsk in eastern Ukraine.
The researchers say these sites are used by Russian forces and their allies to process, register, interrogate and detain Ukrainians trying to leave Russian-occupied territory. Those detained can include civilians and prisoners of war.
The Yale School of Public Health's Humanitarian Research Lab (Yale HRL) in collaboration with US State Department-supported Conflict Observatory used open-source information and high-resolution satellite imagery to map them.
According to the report, there is evidence suggesting they were set up even before Russia's invasion of Ukraine began and grew following the capture of Mariupol in April.
"The conditions reported by those released from the facilities examined here can constitute cruel, inhuman, and degrading treatment under international humanitarian and human rights law," the study says, adding that the "conditions include overcrowded facilities, a lack of access to adequate sanitation, insufficient food and clean water, exposure to the elements, denial of medical care, and the use of isolation."
"In some specific instances, the treatment described as having been endured by those released, such as use of electric shocks, extreme conditions of isolation, and physical assault, may potentially constitute torture if proven," the study says.
In a separate press release Thursday, the US State Department described the "unlawful transfer and deportation of protected persons" described in the study as "a grave breach of the Fourth Geneva Convention on the protection of civilians and constitutes a war crime."