The Islamic State have threatened to kill US citizen Peter Kassig.

Mr Kassig is a former US soldier in his mid-20s who went to the region to volunteer in hospitals in Lebanon.

He then set up his own charity to deliver aid to Syrians with an "acute and immediate need" as he put it in one press interview before he was taken hostage.

Mr Kassig called his group Special Emergency Response and Assistance.

It ferried blankets, cooking materials and fuel and food to parts of north Syria where it was needed most in the most dangerous of conditions.

He told TIME magazine in January 2013 how touched he was by the Syrian people he met in refugee camps on the border.

"I did not meet a single man woman or child who could muster a smile and a message of strength and hope that was nothing short of earth-shatteringly humbling," he said.

Speaking to CNN in June 2012 about his decision to go to Lebanon, Mr Kassig said: "The way I saw it, I didn't have a choice. This is what I was put here to do. I guess I am just a hopeless romantic, and I am an idealist, and I believe in hopeless causes."

Lisa Monaco, Homeland Security adviser to the White House, described Mr Henning's murder as "yet another clear example of the brutality of this group".

IS has previously killed two American journalists - James Foley and Steven Sotloff.