Brits Aiden Aslin and Shaun Pinner were detained in April while fighting in Ukraine before appearing in court in the pro-Russia Donetsk People's Republic (DPR) and being sentenced to death
Two Brits who fought in Ukraine have been sentenced to death by pro-Russian forces.
The supreme court issued death sentences for Aiden Aslin, Shaun Pinner and Moroccan-born Brahim Saadoun earlier today, according to Russian state media.
Mr Aslin's family described the news as a 'very upsetting development' and repeated that the captured soldier was not a mercenary.
The three men said they will appeal the decision made by the Russian-backed court in Donetsk People's Republic (DPR) - which they must do within one month.
According to reports, the so-called trial lasted just three days.
Mr Aslin, 28, and Mr Pinner, 48, were detained in April while fighting in Ukraine, before appearing in court in the separatist Donetsk People's Republic (DPR).
They are said to have admitted "training in order to carry out terrorist activities".
Mr Aslin's family said in a statement: "We've heard the news from Donetsk and need some time to take everything in.
"We can only imagine what they are going through right now.
"This is a very upsetting development and we ask that our privacy is respected at this time."
It is understood Mr Aslin's mum Ang Wood found out about the draconian sentence while watching the TV news at the family home in Newark, Notts.
In footage shared by Ria Novosti on social media on Wednesday, a translator can be heard asking Mr Aslin if he would "plead guilty" to an offence, to which he replied: "Yes."
The video appeared to show the two Britons in the dock in the pro-Russian territory's supreme court alongside Brahim Saaudun, a Moroccan national.
Mr Pinner was facing more severe charges after allegedly admitting to "seizing power by force".
A Downing Street spokesman said: "The UK Government is 'deeply concerned' following the death sentences handed to Britons Aiden Aslin, 28 and Shaun Pinner, 48, who were captured while fighting for Ukraine."
The Foreign Office also condemned the exploitation of prisoners of war for political purposes in the wake of the footage.
It said it was working with the Ukrainian government on the issue of British captives.
Foreign Secretary Lizz Truss tweeted: "I utterly condemn the sentencing of Aiden Aslin and Shaun Pinner held by Russian proxies in eastern Ukraine.
"They are prisoners of war. This is a sham judgment with absolutely no legitimacy. My thoughts are with the families. We continue to do everything we can to support them."
After news of the sentence emerged, former Tory minister Robert Jenrick said: "This disgusting Soviet-era show trial is the latest reminder of the depravity of Putin's regime.
"Contrary to the Kremlin's propaganda, Aiden Aslin and Shaun Pinner are not mercenaries.
"They have been living in Ukraine and serving in its armed forces long before Russia's illegal invasion, and as prisoners of war they are entitled to protection under the Geneva Convention.
"The Russian Ambassador should be summoned to the Foreign Office to account for this egrerious breach of the Geneva Convention. No one should think they can treat British citizens like this and get away with it."
Hours earlier, the MP said his former constituent Mr Aslin should be returned home at the earliest opportunity, possibly through a prisoner exchange.
Mr Jenrick condemned the "trumped-up charges" faced by both Britons and accused Russia of a "completely outrageous breach of international law".
Mr Jenrick told BBC Radio 4's World At One programme: "This is a British citizen, but who also holds Ukrainian nationality, is married to a Ukrainian, joined the Ukrainian armed forces in the normal way prior to (Vladimir) Putin's illegal invasion, and has been serving in the armed forces.
"He was taken prisoner by Russian forces and in accordance with international law and the Geneva Convention, he should be being held appropriately and returned to Ukraine at the earliest possible opportunity, possibly through a prisoner exchange.
"Instead of that Putin's regime have chosen to put him and another British national, Shaun Pinner, on trial on trumped up charges, no evidence whatsoever.
"This is, I'm afraid, a completely outrageous breach of international law and it should be condemned."
He added: "What I hope happens is that a prisoner exchange occurs in the near future.
"The Russian authorities have chosen to make an example out of these two British nationals and it is, I think, completely shameful."
On Monday, Dominic Raab said the Foreign Office will "make all the representations" on Mr Aslin's behalf and his family have also issued an emotional statement calling for his release.
They said: "We, the family of Aiden Aslin, wish to ask for privacy at this time from the media.
"This is a very sensitive and emotional time for our family, and we would like to say thank you to all that have supported us.
"We are currently working with the Ukrainian government and the Foreign Office to try and bring Aiden home. Aiden is a much-loved man and very much missed, and we hope that he will be released very soon."Mr Aslin's family have repeated that he is a prisoner of war