By Damon Green: ITV News Correspondent
A family member of British hostage David Haines has told ITV News of their fears for his safety.
They understand David Cameron's position that no ransom can be paid for a British hostage.
But they wonder if any other pressure could be brought against Islamic State who are holding Mr Haines - possibly financial pressure on those backing the group who have taken him prisoner.
What concerns them most is any possibility of an escalation of the military situation.
They worry whether direct military action against IS - possibly air strikes - could have a direct impact on his safety.
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.