Two Britons who were captured by Russian forces while fighting in Ukraine have been sentenced to death, state-owned Russian news agency RIA Novosti has said.

Aiden Aslin, 28, and Shaun Pinner, 48, were captured in Mariupol in April during the intense fight for control of the port city, before appearing in court in the separatist Donetsk People’s Republic (DPR).

It is understood they have admitted “training in order to carry out terrorist activities”.

A third man, Moroccan national Saaudun Brahim, has also reportedly been sentenced to death.

The punishments were handed down by the DPR’s supreme court, RIA said.

The men were found guilty of “mercenary activities and committing actions aimed at seizing power and overthrowing the constitutional order of the DPR”, the Interfax news agency quoted a court official as saying.

They are likely to face a firing squad if the sentence is carried out.

They have a month to appeal and will be doing go, their lawyer said.

The prime minister’s official spokesman said Mr Aslin and Mr Pinner “should not be prosecuted”.

He commented: “We’re obviously deeply concerned by this.

“We’ve said, continually, that prisoners of war shouldn’t be exploited for political purposes.

“You’ll know that under the Geneva Convention, prisoners of war are entitled to combatant immunity, and they should not be prosecuted for participation in hostilities.

“So we will continue to work with Ukrainian authorities to try and secure the release of any British nationals who were serving in the Ukrainian Armed Forces and who are being held as prisoners of war.”

Footage shared previously by RIA on social media appeared to show a translator asking Mr Aslin if he would plead guilty to an offence, to which he replied: “Yes.”

In the video, the two Britons stand in the dock in the supreme court alongside Mr Brahim.

Mr Pinner allegedly admitted “seizing power by force”.

The 48-year-old was filmed in April saying he had been captured while defending Mariupol, his adopted city.

His family stressed at the time that he was “not a volunteer nor a mercenary, but officially serving with the Ukrainian army”.

He told Sky News a few months before that he was on his fourth tour of duty in Ukraine after serving in the British Army for nine years, had lived in the country since 2018 and has a Ukrainian wife.

Mr Aslin’s family said on Tuesday that it was a “very sensitive and emotional time” and that they were working with the Ukrainian government and UK Foreign Office to try to free the 28-year-old.

“Aiden is a much-loved man and very much missed, and we hope that he will be released very soon,” they said in a statement.

The former care home worker joined Ukraine’s armed forces as a marine in 2018, has applied for citizenship, and has a Ukrainian fiancee.

Former Conservative cabinet minister Robert Jenrick has condemned what he called “trumped-up charges” faced by the British pair and accused Russia of a “completely outrageous breach of international law”.

Referring to Mr Aslin, Mr Jenrick told the BBC: “This is a British citizen, but who also holds Ukrainian nationality, (who) 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.”

Deputy Prime Minister Dominic Raab said on Monday that the British government expected “the laws of armed conflict to be represented” and the Foreign Office would make “all the representations”.