Amnesty International has accused both the Ukrainian Security Forces and separatist groups of committing war crimes, including torture and summary killings of prisoners on a near-daily basis in eastern Ukraine.
In a new report, entitled 'Breaking Bodies: Torture and summary killings in eastern Ukraine,' the organisation provides detailed evidence of frequent and widespread prisoner abuse by a broad range of captors on both sides of the conflict.
Former prisoners have alleged that they were beaten until their bones broke, tortured with electric shocks, kicked, stabbed, hung from the ceiling, deprived of sleep for days, threatened with death, and denied urgent medical care.
Amnesty International Europe and Central Asia Programme director John Dalhuisen said: "Prisoners on both sides have been beaten and subjected to mock executions.
"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."
Held captive between July 2014 and April, the 33 former prisoners interviewed by Amnesty described severe beatings or other serious abuse carried out by both separatist and pro-Kyiv military groups, including the Security Service of Ukraine.
The organisation authenticated the victims' testimonies against additional evidence, such as X-rays of broken bones, hospital records, photographs of bruises and other injuries, scars, and missing teeth.
According to the report, the majority of the worst abuse cases took place in informal places of detention, and during the initial days of captivity, while the situation was found to be particularly chaotic on the separatist side, with a variety of different groups holding captives in at least a dozen known locations.
In addition, Amnesty claims that the two sides are arbitrarily holding civilians who have not committed any crime, but sympathise with the opposing side.
Dalhuisen said: "Pro-Kyiv and separatist forces alike must put an end to these crimes and ensure that all fighters under their control are aware of the consequences under international law of abusing prisoners amid an armed conflict.
"The Ukrainian authorities must investigate all allegations of war crimes and other abuses, open files and collect evidence of abuses by separatist forces and bring to justice all those responsible for perpetrating such heinous acts."