The sister of the British surgeon Dr Abbas Khan who died in Syria said that the Prime Minister has sent the family letters.
Sara Khan told ITV News that David Cameron said "he is now going to help us get answers but nothing has actually been said as to how they expect to do this and when".
David Cameron has written to the mother of a British doctor who died in custody in Syria, describing his death as "a sickening tragedy".
The mother of British doctor Abbas Khan, who died after 13 months in a Syrian prison, has accused the regime of "murdering" her son.
Relatives of British surgeon Dr Abbas Khan have said they do not understand what led to his death just days before he was due to be released