Paul Urey, a British aid worker captured in Ukraine by pro-Russian forces, has died in captivity, an official in the self-proclaimed Donetsk People’s Republic (DNR) said.

Urey, 45, was captured near Zaporizhzhia in April. He and fellow British aid volunteer Dylan Healy were charged with “mercenary” activity, an offense punishable by death in the DNR.

He died Sunday, DNR human rights ombudsperson Daria Morozova said in a post on the Telegram messaging app, citing chronic illness and stress as the factors behind his death.

The British government voiced alarm over the announcement.

“They’re clearly alarming reports and our thoughts are with his family and friends”, - a Downing Street spokesman said.

A DNR court sentenced British military volunteers Aiden Aslin and Shaun Pinner to death last month on the same “mercenary” charges.