LONDON: The UK government said Thursday it was “disturbed” by Ukraine’s claims that a British aid volunteer who died while imprisoned by Russian-backed separatists may have suffered “unspeakable torture”.

“We are disturbed by reports that aid worker Paul Urey may have been tortured in detention,“ the Foreign, Commonwealth and Development Office said in a statement sent to AFP.

“It is essential that we see the results of a full post-mortem as soon as possible,“ the ministry said.

It added: “Our thoughts are with Paul Urey’s family at this distressing time.”

Ukraine’s Foreign Minister Dmytro Kuleba tweeted Wednesday that Russians had returned the body of Paul Urey, with “signs of possible unspeakable torture”, which he said would be “a heinous war crime”.

Urey went out as a volunteer to help evacuate Ukrainians soon after Russia's invasion in April.

He was captured later that month and died on July 10 while being held by Moscow-backed separatists, who said he had chronic illnesses and a “depressed psychological state”.

The death of the father-of-two with Type 1 diabetes was discussed by the UN Security Council and the Organization for Security and Co-operation in Europe.

Then-UK foreign minister Liz Truss said in July she was “shocked” by reports of Urey’s death. She said the Kremlin was “fully responsible” since he was “in custody of a Russian proxy in Ukraine”.

His mother Linda Urey wrote on Facebook Thursday that her son’s body is in Kyiv. She urged supporters “to help me get him back”.

His daughters, aged 17 and 20, are using crowdfunding to pay to repatriate his body.

Russia declined any responsibility for Urey's death, saying Britain should have negotiated with the separatists.

The separatists claimed that Urey, from Warrington in northwestern England, was a professional soldier acting as a mercenary.

Urey was detained at a checkpoint near the southeastern city of Zaporizhzhia and held in the Donetsk separatist region in eastern Ukraine.

Another British man captured with him, Dylan Healy, is on trial in Donetsk with four other foreigners, accused of being a mercenary and facing a possible death penalty. - AFP