A Russian military court Wednesday sentenced a Ukrainian soldier to 19 years for allegedly shooting a civilian he suspected of being a Russian infiltrator in Mariupol last March.

Russian investigators said Anton Cherednik, a member of Ukraine's naval infantry, killed one man in the southern Ukrainian city -- which was under siege by Russian forces at the time -- after stopping two civilians while on a patrol.

Russian forces launched an intense assault on Mariupol, a port city home to more than 400,000 people before the conflict, destroying large swathes in weeks of air strikes, shelling and gun battles at the start of the conflict last year.

Russia's southern district military court in the city of Rostov-on-Don on Wednesday found Cherednik guilty of "murder", trying to "violently seize power", the "use of prohibited means and methods of warfare" and committing a "terrorist act".

It sentenced him to 19 years -- the first three in prison, and the rest in a Russian penal colony.

Prosecutors said Cherednik shot one of the men after an exchange about a Ukrainian type of bread, "palyanitsa", an unfamiliar and difficult word for Russians to pronounce.

In interrogations, he acknowledged shooting the man, but said it was because he had flinched as if he was going to pull out a weapon, not because he had incorrectly pronounced the word, as Russian media reported.

At Wednesday's court session, Cherednik sat in a glass dock at the front of the cage, with a shaved head and in dark clothes.

He had pled guilty to murder, but rejected the other charges against him and intends to appeal the sentence, his lawyers told Russian media after the ruling.

Russia took thousands of Ukrainian soldiers captive after the fall of Mariupol, with some sent to Russia and others held in occupied eastern Ukraine.

On Tuesday, Russian-installed authorities in eastern Ukraine sentenced four other captive Ukrainian soldiers to long sentences for alleged violence against civilians during the battle for Mariupol last year.

Ukraine has also tried and sentenced a number of Russian soldiers on charges of war crimes committed during the conflict.