The crimes have been committed as "part of widespread and systematic attacks on the civilian population and in accordance with a coordinated state policy", writes the independent commission that has investigated the war in Ukraine in a report.
It is unusual for a UN body to express itself in such harsh terms.
According to the report, a large number of civilians have been arrested in areas that have come under Russian control, and many of them have been transferred to prison camps in the occupied parts of Ukraine or in Russia.
Torture and sexual violence
Russian authorities have since continued to commit abuses and crimes against them: many have been missing for months and years, and some have died in captivity.
The Russians have systematically failed to provide information about the fate of the arrested civilians, the report notes.
Even prisoners of war have been tortured and taken away in violation of international law.
Torture has been used systematically to obtain information and intimidate prisoners of war. The most brutal torture has taken place during interrogations, when Russian authorities have also "systematically used sexual violence against male prisoners".
Killing prisoners of war
Increasingly, Russian forces are killing or injuring Ukrainian soldiers who have been captured or surrendered, which constitutes a war crime.
"Testimonies from soldiers who have deserted from the Russian military's armed forces indicate that there is a policy of not taking prisoners of war but instead killing them", the report states.
The commission was set up by the UN Human Rights Council in March 2022, about a month after Russia's full-scale attack on Ukraine. The report will be presented to the council on Tuesday.
