US President Barack Obama has offered his condolences to the parents and family of Abdul-Rahman Kassig

The US aid worker- also known as Peter - was killed by Islamic State militants after being abducted in Syria last year.

US authorities have confirmed a video claiming to show his murder is genuine.

President Obama has called his death an act of "pure evil" by a terrorist group.

Haras Rafiq, from the British counter-terrorism think tank The Quilliam Foundation, has been examining the video which show Mr. Kassig's death: