The routine torture by Russian forces and their affiliates of detainees during their half-year occupation of the eastern Ukrainian city of Izyum was part of a "policy and plan," Human Rights Watch (HRW) said in a statement on October 19.
Izyum, in the Kharkiv region, was taken by Russian forces after Russia's unprovoked invasion in February, and was liberated by Ukrainian forces last month.
A mass burial site was found last month near the city and hundreds of bodies were exhumed, including 30 with signs of torture.
"Russian forces and others operating under their command routinely tortured detainees during their six-month occupation of Izyum," Human Rights Watch said.
HRW interviewed more than 100 survivors who described being subjected to electric shock, waterboarding, severe beatings, threats at gunpoint, and being forced to remain in stress positions for long periods of time.
Survivors identified at least seven locations in Izyum, including two schools, where they said soldiers had detained and abused them.
"The cruel violence and abuse in Izyum were not random incidents,HRW's Belkis Wille said.
"Multiple victims shared credible accounts with us of similar experiences of torture during interrogation in facilities under the control of Russian forces and their subordinates, indicating this treatment was part of a policy and plan," Wille said.
The detainees, who were snatched from their homes or from outdoor locations, were held for up to 14 days.
All male detainees said they were given electric shocks or beaten with hands, rifle butts, metal pipes, and other various objects, and a female detainee told HRW she was beaten with fists and threatened with rape.
"Our findings indicate that Russian troops have committed horrific abuses in many areas they have occupied, and there is real concern about similar abuses in other areas they continue to control," Wille said.
Last month, UN investigators concluded that war crimes had been committed by Russian forces in Kyiv suburbs such as Bucha and Irpin in the early days of Moscow's unprovoked invasion of Ukraine.
