A friend of Steven Sotloff and James Foley has said that reports of delays in a rescue mission for US hostages and journalists "probably cost them their lives".
Documentary film maker Matthew Van Dyke also criticised the US for not paying ransoms for hostages and the American administration's choice of policy decisions in tackling the rising threat of the Islamic State.
He said: "It's time that we look in this particular case of paying the ransoms and getting these Americans home.
"I blame ISIS for their deaths, but this administration hasn't gotten them home. Apparently they dragged their feet on the rescue missions. They haven't paid the ransoms.
"The rise of ISIS didn't have to happen. This is a consequence of a series of policy decisions that now have cost two close friends of mine their lives and will likely cost other hostages their lives as well. It needs to stop."
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.