A British man released by Russia has said he was "treated worse than a dog" and kept in solitary confinement for five months.
Aiden Aslin has returned to the UK after being detained for months following his capture by Russian-backed forces in Ukraine.
Speaking to the Sun on Sunday, he said after being stabbed he was asked if he wanted a quick or "beautiful death".
He said the prisoners had to sing the Russian national anthem every morning.
"And if you didn't sing it, you would get punished for it. You would get beaten," he said.
In the interview, the former prisoner said he was stabbed during his time being held captive – and beaten because of his tattoos.
Ten detainees, including Mr Aslin, were released on Wednesday evening after Saudi Arabia said it had brokered an exchange between Russia and Ukraine.
Among them were five British nationals who were freed – including John Harding, Dylan Healy, Andrew Hill and Shaun Pinner.
Mr Aslin from Newark, Nottinghamshire was held in April while fighting in the south-eastern city of Mariupol.
He, Mr Pinner and a Moroccan national, Brahim Saadoun, were put on trial in the self-declared Donetsk People's Republic and told they faced the death penalty.
Referring to a time he was stabbed in the back with a knife, Mr Aslin said: "I knew there was a very high possibility I was about to be killed."
He was then asked by a Russian who was guarding him: "Do you want a quick death or a beautiful death?"
Answering a quick death, Mr Aslin was told: "You're going to have a beautiful death and I'm going to make sure it's a beautiful death."
He said he was beaten for having a tattoo of a Ukrainian trident and for one showing his time in Syria.
Mr Aslin said he was kept in a two-man cell with four people and had to sleep on a mat infested with lice.
"We couldn't go to the toilet properly because we didn't have a toilet", he said, adding that they had to use empty bottles.
Mr Aslin said he survived for three weeks eating pieces of bread and water – and "eventually we had to beg them to give us tap water".
There was a window in the cell, but it had "nothing to protect us from the outside elements" he said, which led to it being cold in the winter.
Talking about when his passport was checked, "as soon as I said Great Britain I got a straight punch to the nose" he said.
Mr Aslin said the only time he was let out was to do propaganda or take phone calls.
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