(Reuters) - Two Britons and a Moroccan who were captured while fighting for Ukraine could face the death penalty after pleading guilty in a court of one of Russia's proxies in eastern Ukraine, Russia's RIA news agency reported.

       Video published by RIA showed Britons Aiden Aslin and Shaun Pinner and Moroccan Brahim Saadoun in a courtroom cage with white bars.

       RIA said Pinner and Saadoun had pleaded guilty to actions aimed at the violent seizure of power.

       The video appeared to show Aslin pleading guilty to a lesser charge involving weapons and explosives. He was seen standing in the cage and leafing through a sheaf of legal documents as the charge was translated to him.

       The news agency quoted prosecutors as saying the combined charges could mean the death penalty for all three.

       Britain's Foreign, Commonwealth and Development Office did not immediately respond to an emailed request for comment late on Wednesday.

       Saadoun was arrested in April. No comment was immediately available from the Moroccan foreign ministry on his case.

       The trial is taking place in the Donetsk People's Republic, one of two breakaway Russian-backed entities in the Donbas region of eastern Ukraine which Russia says it is fighting to "liberate" from Ukrainian forces.

       Three days before launching its Feb. 24 invasion of Ukraine, Russia recognised them as independent states in a move condemned by Ukraine and the West as illegal.

       Aslin and Pinner were captured in April while fighting on the Ukrainian side. They were later shown on Russian TV asking to be freed in exchange for a Ukrainian ally of Russian President Vladimir Putin who had been detained by Ukrainian authorities.

       Russia said at the time they were being fed, watered and given necessary help.

       (Reporting by Mark Trevelyan; Editing by Howard Goller)