British Prime Minister David Cameron has described the murder of UK aid worker Alan Henning is “completely unforgivable”.
The 47-year-old taxi driver is the latest hostage to be beheaded by the Islamic State militant group (or ISIL).
A video purporting to show Mr Henning being beheaded has been uploaded to Social Media on Friday evening.
Cameron vowed to track down his killers and said the UK government will use all available means to locate other hostages being held by the jihadists.
“What we see with this organisation is that there is no level of depravity to which they will not sink. No appeals made any difference,” he said, referring to a video plea by Henning’s wife made last week.
“The fact that this was a kind, gentle, compassionate and caring man who had simply gone to help others, the fact they could murder him in the way they did shows what we are dealing with, and this is going to be our struggle that with others we must do everything we can to defeat this organisation,” Cameron added.
Henning was kidnapped in Syria last December after raising funds for refugees displaced by the civil war.
RAF Tornados have been striking ISIL targets this week but its unclear whether Britain’s role in the international fightback will be stepped up in the light of his killing.
ISIL militants are still thought to be holding another ten or so westerners hostage as well as hundreds of Syrians and Iraqis.