They Were Captured by the Russians. Then the Hardest Fight Began.

Shot through the jaw and tongue by a sniper’s bullet last year in the last days of the grinding siege at the Azovstal steel plant in Ukraine, Senior Sgt. Maksym Kushnir could not eat or talk, and could barely breathe.

But when he hobbled out of a bunker last May with hundreds of other wounded Ukrainian soldiers in a surrender negotiated with Russian forces, there was no medical help or any sign of the Red Cross workers they had been promised.

Instead, Sergeant Kushnir, nine years a soldier and a poet since childhood, said he was taken on a two-day bus journey into Russian-controlled territory and left on a bed to die, with his jaw shattered and gangrene spreading across his tongue.

“I thought it was the end,” he said. “For the first three to four days, they did not do anything. They expected me to die on my own.”

That Sergeant Kushnir survived and returned home to tell the tale is one of the success stories of the war. Even as the two sides are locked in full-scale conflict, Ukrainian and Russian officials have been exchanging hundreds of prisoners of war almost weekly.

Yet the prisoner exchanges have also revealed a grim reality. Ukrainian soldiers have come home with tales of appalling suffering in Russian captivity — executions and deaths, beatings and electric shocks, a lack of health care and near-starvation rations.

Ukraine allows the International Committee of the Red Cross access to the Russian prisoners of war it is holding, an indication that it is meeting its obligations under international conventions of war. Russia does not. It restricts outside monitoring and has confirmed the identities of only some of those it is holding.

Ukrainian officials and former prisoners say Ukrainian captives were in a visibly worse state than the Russian prisoners at exchanges.

“We were skinny like this,” Sergeant Kushnir said, holding up his little finger. “Compared to us, they looked well. We were thin and bearded. They were shaved and washed.”

“It’s a classic abusive relationship,” said Oleksandra Romantsova of the Center for Civil Liberties, a Ukrainian organization that was awarded the Nobel Peace Prize last year, summing up the treatment of Ukrainian prisoners.

It is unclear how many Ukrainian soldiers are prisoners of war or missing in action. Russia has provided only partial lists of those it is holding, and Ukraine does not release any numbers. But human rights organizations say there are at least 8,000 to 10,000 prisoners, and Ukrainian officials did not dispute those figures.

And more Ukrainians have been taken in the fighting in and around the city of Bakhmut in recent months, according to people working to bring prisoners home. There are believed to be far fewer Russians held by Ukraine.

Some Ukrainian soldiers have also been placed on trial in Russia on dubious charges, and have received lengthy sentences in the Russian penal system, said Oleksandr Pavlichenko of the Ukrainian Helsinki Human Rights Union.

Five hundred medical personnel and hundreds of female soldiers and wounded are among the prisoners of war, said Andriy Kryvtsov, the chairman of Military Medics of Ukraine. He said 61 military medics remained in captivity and called for their release.

Dr. Yurik Mkrtchyan, 32, an anesthetist, was among more than 2,000 taken prisoner after battles at the Ilyich steel plant in Mariupol in April last year, many of them wounded soldiers he was caring for.

He said the Russians provided medical assistance only when he begged them and transferred the wounded to a hospital only when they were close to death.

Dr. Mkrtchyan, who was released after a prisoner exchange in November, said he remained anxious about the conditions of the wounded, including amputees.

“They were just the boys who protected our hospital,” he said. “Most of them are still in captivity, and I see no excuse or explanation for that because they are already disabled, they cannot fight, there is no reason to keep them in prison.”

Former prisoners and human rights groups say Ukrainian captives, including the wounded and pregnant female soldiers, have been subjected to relentless beatings.

Dr. Mkrtchyan described how new arrivals had to run a gantlet of prison guards who beat them with sticks, a hazing ritual known as a “reception.” He recalled running, head down, through the torrent of blows, and seeing a fellow prisoner on the ground. The soldier, a wounded prisoner with serious burns named Casper, was killed by the beating, he said.

Maksym Kolesnikov, 45, was among more than 70 Ukrainian soldiers and four civilians who were captured in the days just after the Russian invasion in February 2022, when Russian troops overran his base near the town of Hostomel, north of Kyiv, Ukraine’s capital.

The men were taken for interrogation to a filtration camp in a disused factory, where their commander was beaten within earshot of the whole unit. The Russian network of filtration camps, where military and civilian Ukrainians are screened and interrogated, have been widely criticized for violations of human rights.

After a few days, Mr. Kolesnikov and his fellow detainees were moved to a Russian prison in the Bryansk region, near the Ukraine border.

The “reception” beating lasted five hours. “I was kneed in the face,” he said. The beatings continued daily for a month. The guards used rubber truncheons, plastic piping, wooden rulers and knotted pieces of rope, or just kicked prisoners, he said.

Prisoners nicknamed one group of guards “the electricians” because they tormented prisoners with electric shocks.

The captives were dangerously malnourished, Mr. Kryvtsov said.

“It was a good day when you found a potato in your soup,” said Mr. Kolesnikov, who added that he lost about 75 pounds in captivity.

He said he suffers from a compressed spine from malnutrition, and hip and knee injuries from the prolonged beatings.

Oleh Mudrak, 35, the commander of the First Azov Battalion, was unrecognizable and painfully thin when he returned from four months in captivity after being taken prisoner at the Azovstal plant in Mariupol, said his nephew Danylo Mudrak.

He regained the weight and underwent surgery on his shoulder, but five months after his release, he died of a heart attack, Danylo Mudrak said.

Members of the Azov battalions, long painted as neo-Nazis by Russia as part of its justification for the war, came in for especially harsh treatment, according to Maj. Dmytro Andriushchenko, who was a deputy commander of the Second Azov Battalion when he was taken prisoner at Azovstal. “Azov was like a red rag for them,” he said.

Major Andriushchenko was in a penal colony at Olenivka in July when an explosion ripped through a barracks, killing at least 50 Azov members. Like several former inmates of Olenivka who were interviewed, he accused Russia of orchestrating the explosion.

The prison guards closed the gates to the barracks, preventing survivors from escaping, Major Andriushchenko said.

Dr. Mkrtchyan, who was in the same penal colony, said he and other Ukrainian medics urged the guards to let them help the wounded, but they were not allowed out of their building.

Russia has blocked calls for an independent investigation into the explosion and blames it on a Ukrainian strike.

For some of the wounded from Azovstal, visits by Russian television crews may have been a lifeline. The publicity created pressure on the Russian authorities to care for the prisoners, who were already weak from their time under siege in Azovstal with little food and water, Sergeant Kushnir said.

With his broken jaw and gangrenous tongue, Sergeant Kushnir could not lie down and sat with his head in his arms for several days without painkillers or antibiotics.

Eventually, he was moved to another hospital where doctors amputated his tongue and wired his jaw closed.

He dreamed of eating. He wrote some verse:

“Have mercy on me, fate. I’m alive.

Don’t punish me mercilessly.”

The physical pain was not as hard to bear as the uncertainty of being a captive, he said.

“When you don’t know what to prepare for, what the next day will bring,” he said, “especially after seeing what the Russians were doing to our men, and being in constant expectation of death, it is not a cool feeling at all.”

At the end of June, Sergeant Kushnir and other wounded men from Azovstal were loaded onto buses and driven to the front line to be exchanged.

Back in Ukraine, he has been through multiple operations and spent months learning to talk again by exercising the scar tissue at the back of his throat.

His surgeon, Dr. Vasyl Rybak, 44, the head of the department of rehabilitation and reconstructive surgery at a hospital in Odesa, took bone from his hip to reconstruct his jaw, but when that did not work, he inserted a titanium jaw, created at a 3-D printing lab in the city of Dnipro.

Next, Dr. Rybak plans to learn from pioneers in India how to create a new tongue for his patient from muscle tissue in his chest.

“He’s a hero,” he said of Sergeant Kushnir, during a break after surgery. “They all are.”

Oleksandr Chubko and Dyma Shapoval contributed reporting.