David Cameron has said he will tonight warn fellow Nato leaders that they must halt ransom payments to terrorist kidnappers.
At a dinner for alliance leaders at the Nato summit in Wales, the Prime Minister will remind them of commitments they have made at the G8 to stop such payments.
He will warn that they simply fuel further terrorist violence, putting their own populations at risk.
"It is utterly self-defeating. It is worse than self-defeating, it is actually a risk to us back at home," Mr Cameron said shortly before the dinner.
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.