UK non-profit organisation Presidium Network raised the alarm when contacts had not heard from the pair since Monday, and the woman they had been trying to help leave received "strange text messages".

Five British prisoners of war released by Russia as part of an exchange with Ukraine have arrived back in Britain and are looking forward to spending time with their families, non-profit organisation Presidium Network said on Thursday.

Two British aid workers who have reportedly been captured by Russian forces in Ukraine have been named. Presidium Network, a UK-based company that says it carries out evacuations of families and individuals from war zones, identified Paul Urey and Dylan Healy as the captured men.