Russian forces and their proxies in Ukraine are operating 21 locations in the war-torn country to hold, interrogate and detain troops and civilians, a report said on Thursday.
The report, published by Yale University researchers with the State Department's backing, used satellite imagery and an open-source data collection to identify the locations.
They included schools in the villages of Bezimenne and Kozatske, municipal centres in Manhush and Nikolske, and prisons in Makiivka and Olenivka.
The Yale School of Public Health's Humanitarian Research Laboratory responsible for the report is a partner in a State Department-funded Conflict Observatory programme.
It was launched this year to analyse evidence of war crimes believed to be perpetrated by Russian forces in Ukraine.
“We again call on Russia to immediately halt its filtration operations and forced deportations, and to provide outside independent observers access to identified facilities and forced deportation relocation areas within Russia-controlled areas of Ukraine and inside Russia,” the State Department said on Thursday.
The large-scale system, researchers say, puts civilians through a registration and interrogation process before releasing them, holding them in detention or sending them to Russia.
The report mainly focused on the region of Donetsk and the Volnovakha Correctional Colony, the prison complex near Olenivka where more than 50 prisoners of war were allegedly killed in a blast there in July.
Ukrainian President Volodymyr Zelenskyy at the time denounced the attack as a “deliberate mass murder of Ukrainian prisoners of war”.
The report says the Volnovakha Correctional Colony near Olenivka is a long-term detention centre for soldiers captured after Moscow forces took the Azovstal steel plant in Mariupol.
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The conditions of the prison includes inhumane treatment of prisoners of war and breach human-rights law, the researchers said.
“Reports include claims of overcrowded cells, insufficient room to lay down, little or no access to water and hygienic facilities, insufficient and irregular nutrition, beatings and torture,” the report said.
Researchers identified two distinct markings along the south and south-west sections of the Volnovakha Correctional Colony that could include mass graves.
Secretary of State Antony Blinken said the US has estimated between 900,000 and 1.6 million Ukrainian civilians have been detained or forcibly deported.
“President [Vladimir] Putin and his government will not be able to engage in these persistent abuses with impunity," the State Department said.
"Accountability is imperative, and the United States and our partners will not be silent."
Russia has denied intentionally attacking or detaining civilians since its February 24 invasion, which it calls a “special military operation”.