Two Britons have been charged with mercenary activities by investigators in a Russian-backed separatist-held territory in eastern Ukraine, according to Russian state news agency TASS.
TASS cited a source in the power structures of the self-proclaimed Donetsk People's Republic DPR, recognised only by Russia and Syria, as saying criminal cases had been opened and charges were filed against Britons Dylan Healy and Andrew Hill.
Both men were refusing to cooperate, it said.
Westerners have been traveling to Ukraine to help defend it against the Russian invasion or to help provide humanitarian aid to millions of Ukrainians whose lives have been up-ended.
On April 29 Russia's defence ministry released a video showing an injured British man captured in Ukraine, who said his name was Andrew Hill and spoke with a British accent, questioned by unidentified Russian forces.
The ministry said he had surrendered to Russian troops in the Mykolaiv region of south-western Ukraine, at least 80 kilometres west of the DPR, and had been carrying a weapon.
The captured man, who was wearing a camouflage uniform, told his questioners he was from Plymouth in southern England and had four children and a partner.
Two Britons and a Moroccan were sentenced last month to death for mercenary activities after being captured fighting for Ukraine against Russia and Russian forces, in what Western politicians decried as a show trial.
Their relatives say they were contracted to fight for the Ukrainian army, so they were not mercenaries but regular soldiers entitled to the protection of the Geneva Conventions on treatment of prisoners of war.
Russian state news agency TASS reported on Friday that the DPR Supreme Court had received appeals from lawyers for Brahim Saadoun and Shaun Pinner, but the other Briton Aiden Aslin had yet to submit an appeal.
The appeals would be considered within no more than two months, according to the court.
It said Mr Pinner had asked for his sentence to be commuted to life imprisonment.
The death penalty will start in 2025, according to a revised criminal code, which took effect on Friday, and was published on a DPR website.
It is not clear what this means for the three men.
The DPR, unlike Russia, has had capital punishment on its statutes since 2014, but hasn't had a legislation outlining how to enforce it until now.
Britain has not been able to deal publicly with Russian proxy authorities in the DPR that it does not recognise, preferring to ask Kyiv for help.
Russia has said that the fate of the men is a matter for the DPR.