LONDON (REUTERS) - The family of Briton Shaun Pinner, who has been sentenced to death by a Russian proxy court in Ukraine's Donbas region, have spoken of their devastation at the news and requested that he be exchanged or released.

Mr Pinner and another Briton, Mr Aiden Aslin, were convicted of mercenary activities by a court on Thursday (June 9) in the self-proclaimed Donetsk People's Republic, which is not recognised internationally.

Mr Pinner's family said the proceedings were an "illegal show trial", and that Mr Pinner should have access to independent legal advice.

"Firstly, our whole family is devastated and saddened at the outcome of the illegal show trial by the so-called Donetsk People's Republic," the family said in a statement.

"Shaun should be accorded all the rights of a prisoner of war according to the Geneva Convention and including full independent legal representation. We sincerely hope that all parties will cooperate urgently to ensure the safe release or exchange of Shaun," they said.

Britain has called the court's decision a "sham judgment", and condemned Russian proxy authorities in Donbas for what it called an "egregious breach" of the Geneva Convention.

The two men were captured during the battle for the port city of Mariupol, one of the bloodiest of the conflict that broke out when Russian troops invaded Ukraine in late February.

Mr Pinner's family said he was a legitimate member of the Ukrainian army after being a resident of Ukraine for the last four years.

"Our family, including his son and Ukrainian wife, love and miss him so much and our hearts go out to all the families involved in this awful situation," the family said.