Islamic State (IS) on Sunday released a video purporting to show the beheading of US aid worker Peter Kassig and several captured Syrian soldiers.

The White House condemned the purported killing and said the US intelligence officials were working to determine the authenticity of the video.

The footage is showing a man dressed in a black robe and carrying a mask over his face in the aftermath of a beheading with the identity of the victim not clearly recognizable.

In comments addressed to US President Barack Obama, the militant claims the head shown in the video is that of "Peter Edward Kassig, a US citizen of your country, who fought against the Muslims in Iraq while serving as a soldier in the American army".

"If confirmed, we are appalled by the brutal murder of an innocent American aid worker and we express our deepest condolences to his family and friends," US National Security Council spokeswoman Bernadette Meehan said in a statement.

Kassig served in Iraq in 2007, and travelled to Syria as an aid worker last year. He was kidnapped and taken hostage by Islamic State militants in northern Syria in October 2013.

Kassig is the fifth Westerner appearing to have been beheaded by the Islamist jihadists. US journalists James Foley and Stephen Sotloff, as well as British aid workers David Haines and Alan Henning have appeared on videos released by Islamic State purportedly showing their beheading.

Unlike those videos, Sunday’s footage didn't show Kassig alive and didn't include a threat to another hostage. Islamic State threatened to kill Kassig in a video appearing to show the beheading of Alan Henning last month.

Sunday’s video, posted online by several social media accounts known to be affiliated to the Islamist group, also showed what appeared to be the mass beheading of several captured Syrian soldiers by separate militants.

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