Russia and pro-Russian separatist forces in Ukraine operate 21 sites to detain, interrogate and process prisoners of war and civilians, according to a new report by Yale University researchers supported by the US State Department as part of efforts to hold Moscow accountable for the war. crimes, reports Reuters.

The report, seen by Reuters ahead of publication on Thursday, cited satellite imagery and open-source information to identify with “high confidence” specific locations, including buildings that used to be schools, markets or conventional prisons. It also identifies possible graves from the prison complex.

The Yale School of Public Health’s Humanities Research Laboratory, which produced the report, is a partner in the US State Department-funded Conflict Observatory, which was launched in May to collect and analyze evidence of war crimes and other alleged atrocities committed by Russia in Ukraine.

As a result of the explosion, 53 prisoners of war died

Nathaniel Raymond, the lab’s executive director, said the findings showed Russia and separatists in Ukraine had set up a “filtering system” to sort people out of Russian-occupied territories, which are a “human rights emergency.”

Reports of abuse of these filters have already appeared on various sites, including in the prison complex near Olenivka in Donetsk, where 53 Ukrainian prisoners of war were reportedly killed in an explosion on July 29.

Prisoners of war were forced to dig mass graves

Yale researchers recently discovered ground irregularities that appear to resemble individual or communal pits as early as April, according to a report based on the account of a former inmate who said inmates were forced to dig pits at the time.

Although the researchers did not reach any conclusions about the fate of the Ukrainian prisoners of war in the prison, they also confirmed that other mounds of the complex were captured on July 27, before the Olenivka explosion. The New York Times previously reported such disparities at the complex in July.

“The conditions are absolutely conducive to extreme abuse,” Raymond said, adding that it was not known how many civilians had passed through the checkpoints or were still being held there.

The Russian defense and foreign ministries and the Russian embassy in Washington did not immediately respond to requests for comment.

Ukrainian officials have accused Russia of deporting hundreds of thousands of people from Russian-controlled areas of Ukraine.

Moscow denies that it has deliberately targeted civilians since invading Ukraine on February 24 during what it calls a “special military operation” and says it is offering humanitarian aid to those who want to leave.

In July, the Russian Embassy in Washington said that US claims about the detention of Ukrainian civilians in the occupied territories are an attempt to fuel “Russophobia” and discredit the Russian armed forces.

There are 21 filtering points in Donetsk alone

Thursday’s report focused on Donetsk region, where Russia and the self-proclaimed Donetsk People’s Republic seized control of much of the city of Mariupol in March. In April, the city’s mayor said that about 40,000 of the city’s civilians had been forcibly relocated to Russian-controlled territory or deported to Russia.

The report identifies a system that transports civilians to conflict zones, registers them and interrogates them before they are released, detained or transported to Russia.

The researchers verified 21 sites from at least five independent sources and believe at least seven other sites are part of the filtering system and may be tested later, Raymond said.

In June, the US National Intelligence Council said it had identified 18 possible sites used for the leak in Ukraine and western Russia.

In a statement Thursday, the State Department demanded that Russia end all filtering operations and forced deportations and allow access to outside observers.