Islamic State conflict: Will US respond to Kassig murder?
US President Barack Obama has condemned the killing of US aid worker Abdul-Rahman Kassig as "an act of pure evil".
The Islamic State (IS) militant group released a video on Sunday showing a masked man standing over a severed head, which the White House confirmed was Mr Kassig.
The latest killing is likely to prompt questions over whether the US should take more action against IS.
David Willis reports from Washington.
17 Nov 2014