Ukrainian officials and former detainees said Monday that Russia has carried out a systematic campaign of torture against prisoners of war and civilian detainees, with captives held incommunicado and subjected to beatings, electric shocks and sexual abuse. Thousands of Ukrainians are still believed to be held in Russian custody.

Russia rejected the allegations during an informal U.N. Security Council session. Maria Zabolotskaya, Russia’s deputy U.N. representative, dismissed the claims as a “disinformation campaign” and accused Ukraine of subjecting Russian prisoners to “torture and degradation and moral and physical abuse.”

Khuan Alberto Levya Garsiya, an active member of the Ukrainian military, said his Russian captors subjected him to virtually every form of torture imaginable during his 1,183 days in captivity.

“Yes ... I was tortured,” he told reporters after the U.N. meeting. “Anything you can think of that can be done hurtful, humiliating to a man, unwillingly. Anything that comes to your mind, not only verbal, physical abuse, daily beatings, electrocution, excessive, excessive exercises in freezing cold when it’s minus degrees, sexual abuse. Everything that can be applied to a person into making a person break mentally. It was all applied to me and most of my comrades.”