Prime Minister Liz Truss said five British nationals detained in Ukraine and held by Russian-backed forces are being returned to their families.
“Very welcome news of the safe return of five British nationals held by Russian-backed proxies in eastern Ukraine, ending months of uncertainty and suffering for them and their families,” he tweeted.
Aiden Aslin, a British fighter who was sentenced to death by a pro-Russian court, is among those freed, said his MP Robert Jenrick.
He tweeted: “Aiden’s return ends months of agonizing uncertainty for Aiden’s loving family in Newark who suffered daily from Aiden’s fraud trial but never lost hope. As they are reunited as a family, they can finally live in peace.”
Mr Aslin, 28, moved to Ukraine in 2018 and later joined the country’s armed forces.
The Saudi Foreign Ministry said that Russia released 10 foreign prisoners of war through the mediation of the country’s Crown Prince Mohammed bin Salman.
The list includes American, British, Croatian, Moroccan and Swedish nationals, the ministry said, and a plane carrying the detainees landed in the kingdom.
“Relevant Saudi authorities have transferred them from Russia to the state and are facilitating the process for their respective countries,” the statement said.
The ministry did not reveal the identity of the detainees. A Saudi official said five Britons, two Americans, one Croatian, one Moroccan and one Swedish citizen.
It is not yet known whether the five include Sean Pinner, who was imprisoned with Mr Aslin and sentenced to death in Donetsk, one of Russia’s proxies in eastern Ukraine.
Prince Mohammed has maintained close ties with Russia’s Vladimir Putin, including within the framework of the OPEC+ oil producer group, despite strong pressure from Riyadh’s traditional ally Washington to isolate Russia.
Miss Truss thanked Ukrainian President Volodymyr Zelensky for his “efforts to secure the release of the prisoners and Saudi Arabia for their support”.
“Russia must end its brutal exploitation of prisoners of war and civilian prisoners for political purposes,” he added.
Foreign Secretary James Cleverley said: “This ends months of uncertainty and suffering, including the threat of execution for them and their families at the hands of Russia.
“Sadly this was not the case for one of those detained, and our thoughts are with Paul Urie’s family.”
The British volunteer died earlier this year while being held by Russian-backed separatists.