“On the second day they broke my arm,” Mykhailo Chindey recalls being interrogated by Russian soldiers.

“One person held my hand and another hit my arm with a metal stick. They beat me for two hours almost every day.

“At one point I lost consciousness. I lost a lot of blood. They hit my heels, my back, my legs and my kidneys,” he said.

In the Izyum hospital, Chindey carefully started walking again.

His injured arm is in a cast, a painful reminder of the Russian occupation of the eastern Ukrainian city.

The Russians arrested Chindey after Kiev’s forces bombed a school near his home, killing and injuring “many” occupying forces, he said.

He was suspected of providing Ukrainian soldiers with the coordinates for the attacks. His interrogators insisted that he disclose any communications he had with them.

“They pulled a bag over my head and took me somewhere,” the 67-year-old told AFP. “When I could see again, I recognized the place: it was the police station in Izyum.

Chindey’s experience is just one of several stories of torture and arbitrary arrests by Russian forces that have recently surfaced in eastern Ukraine.

Kiev’s forces took a number of cities in their counter-offensive earlier this month, including Izyum, Balakliya and Kupiansk.

Ukraine’s national police chief said on Friday that more than 10 “torture chambers” had been found in the formerly Russian-controlled parts of the northeastern Kharkiv region.

Ukrainian officials also said they found mass graves after Russian troops withdrew from Izyum.

President Volodymyr Zelenskyy called the Kremlin forces “murderers” and “torturers”.

Chindey showed AFP the tiny, damp cell he said he was held in with up to seven other prisoners for 12 days before Ukrainian troops arrived.

A scrap of his jacket, which he used as a bandage, was stuck to the cell wall in the basement of the bombed-out police station.

Other inmates are held in a dozen cells spread over two floors in the basement, he said.

Chindey recalled seeing about 15 people – and none of them stayed there without being beaten.

“I could hear the other interrogators screaming around the clock,” he said.

A man died there, he added.

On the ground floor, a young officer from Kharkiv, Ukraine’s second largest city, has arrived to investigate possible war crimes.

The office in which he begins writing his report reflects chaos. Folders lie strewn on the floor alongside broken chairs and toppled furniture.

In one room, more than 100 Ukrainian passports lie on the floor, on an old sofa and on a desk.

“We have a lot to do,” admitted the man, who declined to give his name.

Investigators would have to check everything, even digital fingerprints, to match them with those found in the Kiev suburb of Bucha and other locations where potential war crimes were being committed.

Alleged torture cases would be reviewed by investigators who arrived in Izyum on Sunday and they would remain there for four to five days, he added.

Not far from Izyum is Kupyansk, where a panicked Marina Mikhailychenko is trying to flee the non-stop bombardment of the battered city, which is still being fought by both sides.

The 32-year-old said she was arrested and detained for a week during the Russian occupation of Kupyansk because her brother is serving in the Ukrainian army. Eight other people were crammed into their cell.

A volunteer in Kupyansk, nicknamed “Bronik,” told AFP police have arrested and tortured anyone who has fought in the Ukrainian army since 2014 or is pro-Kyiv.

“I don’t know if people died from torture,” he said.

“But there were people who were physically injured. Local residents saw bodies floating in the river.”

In Balakliya, Viktor Priliepov said the Russians held him in a cell at the police station for three days and put a bag over his head.

Priliepov, 68, was questioned about his son in the Ukrainian army but believes he avoided rough treatment because of his “health problems”.

But others, he said, weren’t so lucky.