By Anastasiia Malenko and Yurii Kovalenko

KYIV (Reuters) - Kateryna Bondarenko had little doubt that her boyfriend, a fighter with Ukraine's Azov regiment captured by the Russians in 2022, would receive a long prison term when a military court handed down its sentence.

That did not make it any easier when the news of Oleksii Smykov's punishment came on Wednesday.

"Everyone knew it was going to happen, but everyone was shocked," Bondarenko, 26, told Reuters after the sentencing. "You see the name of your loved one and it says sentenced to 23 years ... It's very destabilising."

Smykov was one of 12 members of the regiment who appeared shaven-headed in court. The defendants all received long sentences, and Russian independent media outlet Mediazona said they intended to appeal.

Bondarenko urged Ukraine's allies to put pressure on Russia to return the fighters, who were defending the Ukrainian city of Mariupol after Russia invaded Ukraine in February 2022.

Russia designated the Azov regiment as a terrorist organisation and the defendants were charged with terrorist activity and violently seizing or retaining power.

Ukraine's human rights ombudsman Dmytro Lubinets accused Russia of violating international humanitarian law because he said the men were combatants, not criminals.

When Smykov, 28, became one of the first Azov fighters to be captured, Bondarenko did not know where to turn to find out what was happening to him.

That changed after hundreds of fighters defending Mariupol surrendered in May 2022, as Russia besieged the city.

Three years later, group chats with relatives of other prisoners make up almost all of her texts.

On Wednesday, her phone buzzed with news from the trial in southern Russia.

"In the video ... he is standing looking at the ground, sullen. He does not know anything at all: that people are fighting for him here, love him, wait for him."

Bondarenko said she hoped he might be included in a prisoner swap, such as those that have taken place during the three year war. Eleven other defendants in the case on Wednesday were convicted in absentia, having already been exchanged in swaps.

"If we don't demand the return of these prisoners, they won't just appear in the exchange," she said, while acknowledging that the conviction now made it more difficult.

She calms herself by thinking about their plans: marriage, children, travel.

"This is not the life I wanted," she said. "I just think about how he feels and I understand that in my position I have nothing to complain about."

(Reporting by Anastasiia Malenko; Editing by Alison Williams)