David Cameron's Government is facing the dilemma of how to respond after Islamic State militants claimed to be holding a British hostage.
While the Prime Minister remains insistent that the country will not pay a ransom, he faces increasing calls to join US airstrikes against the militants.
ITV News Correspondent Paul Davies reports:
I've been told at the Nato summit that the intelligence services know exactly who 'Jihadi John' is - or at least are 99.9% certain.
The British aid worker being held by Islamic State is David Haines, a 44-year-old father-of-two from Perth, Scotland.
In a video statement which claims to record his final words US hostage and journalist Steven Sotloff blames US foreign policy for his death.