LONDON (REUTERS) - British Prime Minister David Cameron said on Saturday he would use "all the assets we have"to try to find hostages being held by Islamic State in Iraq and Syria (ISIS).

Speaking in a broadcast message after the release on Friday of a video showing the decapitated body of British aid worker Alan Henning, Mr Cameron said the whole country was mourning.

"In terms of what we will do, we will use all the assets we have ... to try and find these hostages, to try and help these hostages ... and do everything we can to defeat this organisation which is utterly ruthless, senseless and barbaric in the way it treats people."