Following the death of Steven Sotloff and warnings that a British man could follow, David Cameron has vowed that the Government will not be "cowed" by terrorists.
As ITV News Political Correspondent Carl Dinnen reports, the Foreign Office remains insistent that the latest threats will not change Britain's policy in the region.
Warning: This report does not contain the most distressing images from the IS video, but some may still find its content disturbing
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.