File photo: A Ukrainian serviceman jumps off a tank damaged during fighting with pro-Russian separatist forces.
Amnesty International on Friday accused Ukrainian forces of torture and pro-Russian rebels of even more serious war crimes such as summary executions committed both before and after a February truce deal.
The damning report adds to a growing string of independent findings suggesting that Europe is witnessing the most brutal conflict on its outer border since the 1990s Balkans crises.
"Former prisoners described being beaten until their bones broke, tortured with electric shocks, kicked, stabbed, hung from the ceiling, deprived of sleep for days, threatened with death, denied urgent medical care and subjected to mock executions," the global human rights organisation said in a new report.
Almost daily exchanges of loosely-aimed heavy weapons have killed at least 6,250 people and left nearly two million homeless since the conflict broke out 13 months ago.
Much of the fighting on the pro-Kiev side is being waged by irregular forces who follow their own nationalist commanders and appear to pay little attention to orders coming from the Ukrainian general staff.
Kiev and the West accuse the rebels on the other side of being supported by Russian special forces who provide and often operate long-range rocket systems that have damaged thousands of homes across Ukraine's industrial east.
Both sides have been condemned for indiscriminate bombings.
A joint investigation conducted by Human Rights Watch and The New York Times released in October found several credible cases of Ukrainian forces shelling densely-packed cities with cluster munitions -- a highly destructive weapon banned by much of the world.
Friday's Amnesty report focused on explosive prisoner abuse allegations at the heart of a vicious public relations battle between Russian state television and Ukraine's predominantly pro-Western press.
Its researchers said that 32 of the 33 former detainees interviewed from both sides of the conflict described "severe beatings or other serious abuse".
"Accounts of detainee torture are as commonplace as they are shocking," Amnesty's Europe and Central Asia Programme director John Dalhuisen said.
"Prisoners on both sides have been beaten and subjected to mock executions," said Dalhuisen. "We have also documented summary killings of those held by separatist groups. It is a war crime to torture or deliberately kill captives taken during conflict."
Neither the insurgents nor the various Ukrainian military units issued immediate responses to the report.