
IMAGE SOURCE, GETTY IMAGES Image caption, The city of Zaporizhzhia took in many people fleeing besieged Mariupol, but was also shelled itself
By Joseph Lee
BBC News
The non-profit Presidium Network said Paul Urey and Dylan Healy were detained at a checkpoint in southern Ukraine on Monday.
The Foreign Office is said to be urgently seeking more information.
Mr Urey’s mother said she was extremely worried for his welfare, as he has type 1 diabetes and needs insulin.
The two aid workers are believed to have been working independently, but were in touch with the Presidium Network.
They were said to be trying to rescue a family from a village south of the city of Zaporizhzhia at the time of their capture.
Ms Urey also told Sky News she felt like she was living her “worst nightmare”.
“I just don’t know what to do,” she said.
“I know nothing and just want to get him back.”
Mr Urey’s mother said she knew something was wrong when she did not hear from her son, who usually messages her “20 times a day” and calls via FaceTime “eight to nine times a day”.
Mr Healy is described as a chef by training, originally from Huntington in Cambridgeshire. He was driving the car at the time of the men’s capture, Presidium said.

Presidium Network’s founder, Dominik Byrne, told the BBC it had taken the men six hours of negotiation to get through the last Ukrainian checkpoint and into Russian-controlled territory, where they were detained.
Mr Byrne said he was making an appeal on behalf of the captured men “to get the support we need from the UK government and from the international community, as well as on the ground”.
He said he also wanted “to get clarification about how they are and how safe they are” and to know whether they were being “treated properly”.

On Thursday, the government confirmed that one Briton had been killed in Ukraine and another was missing.
Two other British men, Aiden Aslin, 28, and Shaun Pinner, 48, were captured earlier this month while fighting in the south-eastern city of Mariupol and shown on Russian state TV with apparent facial bruising.
In other developments:
- Foreign Secretary Liz Truss said the UK is sending war crimes experts to help Ukraine investigate allegations of Russian atrocities, including experts in conflict-related sexual violence
- About 8,000 British Army troops and dozens of tanks will take part in exercises across eastern Europe this summer. This is part of a long-planned action which was scaled up after the invasion of Ukraine, the Ministry of Defence said
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