Abdul-Rahman Kassig killing is pure evil, says Obama
US President Barack Obama has condemned the killing of US aid worker Abdul-Rahman Kassig as "an act of pure evil".
The IS militant group released a video showing a masked man standing over a severed head, which the White House confirmed was Kassig.
His parents said he died "as a result of his love for the Syrian people.
Kassig, 26, was taken while working for a refugee group. He is the fifth Western hostage to be killed by IS, which controls parts of Syria and Iraq.