17-year-old Ukrainian describes his experience as a prisoner of war

Vlad Buryak, 17, was traveling in a car on the morning of April 8 and stopped at a Russian checkpoint. Within hours, he would end up in a Russian prison.

Russian soldiers had seen his cellphone and accused him of filming them, he told ABC News' Britt Clennett during an interview held over Zoom. They took his phone and while checking his photos and social media, they found a pro-Ukrainian Telegram group.

The soldiers were furious, he said, and threatened to kill him on the spot. Instead, he was taken to a filtration camp and then to a prison where he would spend 48 days before eventually being released.

Thousands of Ukrainians have reportedly been held as prisoners of war and hundreds of thousands have been forcibly deported from the country through so-called filtration camps.

The experience of children during the war, which has stretched over six months, has been uniquely traumatic and provides a chilling portrait into the painful reality on the ground in Ukraine.

The U.N. estimates that nearly 1,000 children have been killed or injured during the conflict and more than 5 million Ukrainian children, both inside the country and living as refugees, are in need of humanitarian aid.

The prison he was put into "so awful and so difficult," he said, adding that hearing constant cries of "help me" and "don't beat me" breaks you inside.

His job was to wash floors, cleaning rooms that had been used for torture "three or four days a week," he said.

He helped pass information between prisoners, written on small bits of paper which they would try to smuggle outside the prison walls to family members.

He wasn't beaten, but watched other gets beaten and tortured. Although he noticed everything going on around him, he tried to be invisible he said, focusing on his work. He didn't want the Russian soldiers to know how much he was seeing.

During the interview with ABC News, he admitted that he had probably blocked out many aspects of his time in prison. "If you see awful things, your brain forgets it." If he dwells on the past too much, "I can have problem in my head," he said, "and I don't want to have [that]."

So, he said, "I prefer to not think about this."

It was very difficult to maintain his psychological health in prison, he said. If you show emotion, there was the fear of being beaten and tortured, and of never being released, he said.

"If you begin crying, if you begin to be angry with these Russian soldiers, these Russian soldiers can kill you or torture you."

To keep himself mentally sane, he would talk to himself. "I think about what I do when I have freedom. What I do after prison, what I do with my family, how I visit my friends, how I go to the café, how I go to McDonald's," he said.

After 48 days, he was finally reunited with his father.

"You can't explain this emotion," he said, displaying maturity beyond his years. "This emotion you can only feel."