Mykola Vakaruk shows a scar on his body in a small town in the Donetsk region. (AFP)
Secretly detained by Ukrainian authorities for almost 600 days, Mykola Vakaruk suffered repeated beatings, battled the freezing cold and lost a kidney in an ordeal he described as pure hell.
The 34-year-old was released in late July following pressure from rights monitors from Amnesty International and Human Rights Watch, who revealed the existence of "secret prisons" run by the pro-Western former republic's security service.
In their July report, the global rights groups accused both the Ukrainian forces and pro-Russian separatists of illegally holding and torturing civilians in the war-torn industrial east.
The 28-month conflict has claimed nearly 9,600 lives and displaced some two million people. But it has also been accompanied by damning allegations of human rights violations and war crimes committed by both sides.
Vakaruk's life turned into a nightmare in December 2014, when he was arrested by unidentified people in his hometown of Ukrainsk, which borders the war zone but remains under Kiev's control.
With one of his hands handcuffed to a radiator, "the interrogations began," Vakaruk told AFP after finally making it back home.
"Two men in civilian clothing came up to me and said: 'In case of a wrong answer, you will get a blow to the chest'," said Vakaruk, whose thin frame and haggard look betrayed signs of enduring hardship.
Vakaruk said his captors forced him to confess to being "engaged in provocations against the Ukrainian authorities," a euphemism for being a separatist or a rebel supporter.
"It was freezing and the cell was just two square meters (22 square feet)," he said. "Even the water turned into ice."
The repeated blows he sustained severely damaged his kidney, which caused him even further agony in the cold.
In March 2015, he was hospitalised in the Ukrainian industrial hub of Kharkiv, which barely escaped the conflict. In hospital, he was forced to assume a false identity before undergoing surgery to remove his kidney.
He was held by the Kharkiv security service the rest of the time, before being suddenly released on July 25.
"We got our papers back and 100 hryvnias ($3.80, 3.40 euros)," in compensation, he said.
Threats of 'severe repercussions'Between July 25 and August 2, 13 prisoners who were held secretly in Kharkiv by Ukrainian forces were released, Amnesty International and HRW said in a report published last month.
The two groups had earlier denounced the existence of such detention centres -- where they said people were often held without being formally charged -- in the government-held cities of Kharkiv, Kramatorsk, Izium and Mariupol.
Ukraine's security service denied the allegations.
But in May, the United Nations Subcommittee on Prevention of Torture (SPT) was forced to abandon its mission to Ukraine after being denied access to a number of places where people were believed to be detained and mistreated.
A three-member SPT delegation will return to Ukraine on Monday after holding what it said were "positive talks" with Kiev.
But the group's suspended visit and repeated allegations of the security service resorting to torture have tarnished the image of a country that broke loose from Russian influence in a historic February 2014 revolution and has anchored its future to the West.
The pro-Moscow revolt, in which the Kremlin denies any involvement, began weeks after Russia annexed Ukraine's Crimea peninsula in March 2014 -- a step that plunged Moscow's relations with the West to a post-Cold War low.
Ukrainian authorities and the pro-Russian rebels have also held a number of prisoner swaps.
Yet monitors are concerned that civilian detainees were often presented as combatants to be used during these exchanges.
Amnesty and HRW believe that at least five more people were still being secretly held by Ukraine's secret service, a charge Kiev denies, adding that all its conduct was legal.
According to their report, before releasing the prisoners, guards often threatened them with "severe repercussions" if they spoke out about their detention.
But Vakaruk has refused to stay in the shadows, pledging to seek justice with the help of his family.
"Why I should move away from here? My parents are buried here, my children were born here," he said.