This soldier survived the siege of Mariupol and capture by Russia. What about all the others?

When the Russian tank turned its turret toward Hlib Stryzhko's position and fired, he thought his life was ending in a violent flash of light.

"I was aware that I could die, lose my health or become an invalid but I was ready to do it for Ukraine,"he told CBC News.

The corporal in Ukraine's marines had been part of a group of hundreds of soldiers holding off a massively larger Russian force that was attacking the Illichiron and steel works plant in the northern part of the besieged city of Mariupol on April 10.

Somehow,Stryzhko not only survived the tank blast,which left him with horrific injuries,but he also lived through more than two weeks as a prisoner of war in Russia.

Now convalescing in hospital in the Ukrainian capital,Kyiv, he told his story of survival to our CBC News team.

Russia saysit has more than 6,400 Ukrainian soldiers in custody a number that was released before Russian troops seized control of the Donbascity of Severodonetsk last week.Ukraine's government has not said how many of its soldiers have been taken prisoner.

The ferocious battle may have led to the encirclement of even more Ukrainian divisions.

Ukraine has called for their prisoners to be released as part of a prisoner swap, but Reuters News Agency reports Russia's investigative committee is planning to put many of those men including those who defended Mariupol on trial for "crimes against peace."

Human rights groups fear the proceedings will end up being show trials.

Non-Ukrainian soldiers

Russia is also holding a number of non-Ukrainian soldiers as prisoners.Some are soldiers with dual Ukrainian nationalities while others came to Ukraine to join a legion of foreign fighters.

Britons Aiden Aslin and Shaun Pinnerand Moroccan Saaudun Brahim have been sentenced to death by a court in the self-proclaimed Donetsk People's Republic,a decision that has been condemned by the United Nations.

Two former American soldiers who came to Ukraine to fight against the Russians are also now PoWs and there are fears they, too, could be handed death sentences.

For Stryzhko, 25,the decisive moment came as he was on the third floor of the Mariupol building spotting Russian troops when the tank broke through Ukrainian lines and its huge gun fired on his position.

"When a tank shoots, there is no time between the shot and the landing of that weapon, as with artillery," he said from his hospital bed.

In vivid detail, he recalled the thoughts that flashed through his mind as the concrete floor collapsed under him and he began plunging downwards,with rubble and debris all around him.

"It felt as if my fall lasted two, three hours, but actually it lasted less than 10seconds," he said."My brain did not shut down and I talked to God: 'Is this my death in Mariupol,is this how I die?'"

The former history teacher survived the fall but was covered in heavy concrete rubble,breaking so many bones that he says he gave up counting.

Among the worst injuries he suffered were a broken jaw and a broken pelvis.

Turned over as prisoners

Pulled out of the debris by his colleagues,Stryzhko was taken to a temporary Ukrainian field hospital that was already filled with up to 300 wounded soldiers.

Unable to treat them all,the commander eventually signalled to the Russians by waving a white flag that his wounded were being turned over as prisoners,in the hopes they would receive medical care.

What followed for Stryzhko was a three-week odyssey of being moved first to a hospital in Russian-occupied Donbas and then airlifted to another Russian facility in Crimea.

He saidat no time did the Russians treat his injuries or try to ease his pain.

"Every time I was moved, I felt enormous pain.Instead of six people holding my legs, pelvis and head, two people carried me by my legs and my head, and my body was hanging in the shape of a letter V," he told CBC News.

Eventually, on April 28,16 days after he became a PoW, he was among several dozen Ukrainian prisoners who were driven byRussiansto a location in the southern Kherson region where the Ukrainians exchanged themfor Russian prisoners.

'Nobody knows where'

Why he was returned when so many others were left behindremains a mystery, he said,but he presumes it may be because he was so badly wounded that it was deemed unlikely that he could return to the battlefield.

"There were 450 [Ukrainian marines]with me.When we received an order to come out from Mariupol, only 41 people came out. All the others are dead or are in Russian prisons. Nobody knows where,"he said.

Stryzhko said he wanted to tell his story to CBC News in the hopes that the international community can pressure Russia to free the Ukrainian soldiers it has in captivity.

"It's very important for the international community to help Ukraine to put pressure on Russia and let the prisoners of war come back to their families."

Ukraine's government has said very little about the status of its prisoners of war or what it is doing to get them back.

In media comments last week,one of Ukrainian President Volodymyr Zelensky's top security officials,Oleksiy Danilov, refused to discuss prisoner exchanges,calling it an "extremely delicate matter."

A Ukrainian governor said earlier in June that his country had managed to conduct 11 prisoner swaps with Russia since the start of the invasion on Feb.24. There have subsequently been reports of one more exchange,although it was reported it involved Ukrainian civilians,not soldiers.

Aisling Reidy,who tracks prisoner-related issues for Human Rights Watch, saidtrying to understand what has happened to Ukrainian prisoners in Russia has been frustrating and complicated.

"We have stopped reaching out to Russian authorities because it's not getting anywhere," she said.

There have been multiple reports of captured Ukrainians being tortured and mistreated.

What is clear, however, is that Russia has broken many of the normal conventions on dealing with prisoners of war, including putting them on trial on charges for participating in the conflict, said Reidy.

"It's completely outrageous. These are fictitious charges that have no basis in international law," she told CBC News.

"PoWs are capturednot to punish them for the war, but to prevent them from continuing to fight and can lawfully be held until the end of the war, at which time they should be repatriated."

She said Russia has also been holding Ukrainian civilians from territories that its forces have captured and then attempted to trade them for Russian soldiers captured by Ukraine.

She said that essentially amounts to "hostage-taking."

As for Stryzhko, the pins that had been holding his shattered pelvis together have been removed but his mobility is limited.

He is months away from being able to walk again and his days as a combatant are over but perhaps there's still a role he can play.

"I have dreams of putting on my uniform and if doctors allow it, I'll be glad to rejoin the Ukrainian marine corps.If not, then I would like to join any organization that will help bring our victory over Russians closer."