Kassig killing: Obama condemns IS murder of US hostage
President Barack Obama has described as "pure evil" the killing of US aid worker Abdul-Rahman Kassig, whose beheading was shown in a video posted by Islamic State (IS).
The video, authenticated by the White House, shows a masked man standing over Mr Kassig's severed head. It also shows the beheading of 18 Syrian captives
BBC Security Correspondent Frank Gardner reports.