The United States is in mourning for a second US journalist murdered by Islamic State militants, and questions remain over what the country's response should be.
US Vice President Joe Biden used the strongest language of its country's leadership yet, saying the country would chase the militants "to the gates of hell".
Nonetheless, as Washington Correspondent Robert Moore reports, the country's planned response to IS remains unclear:
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.