ISIL beheads British hostage Alan Henning

An Internet video released on Friday purports to show an Islamic State group fighter beheading British hostage Alan Henning, the fourth such killing carried out by the extremist group now targeted in US-led airstrikes.

The video mirrored other beheading videos shot by the Islamic State group, which now holds territory along the border of Syria and Iraq, and ended with a militant threatening a man they identified as an American named Peter Kassig.

“Obama, you have started your aerial bombardment of Sham (Syria), which keeps on striking our people, so it is only right that we continue to strike the necks of your people,” the masked militant in the video said.

National Security Council Spokesperson Caitlin Hayden confirmed that Mr Kassig was held by Islamic State militants.

“At this point we have no reason to doubt the authenticity of the video released earlier today. We will continue to use every tool at our disposal - military, diplomatic, law enforcement and intelligence - to try to bring Peter home to his family,” Ms Hayden said in a statement Friday night.

The video was released in the same manner as other Islamic State group videos and the masked militant sounded similar to the one who carried out the other slayings.

In a statement, the British Foreign Office said it was working to verify the video.

“If true, this is a further disgusting murder,” the statement read. “We are offering the family every support possible; they ask to be left alone at this time.”

Britain has been supporting US military efforts against the Islamic State group by using British forces to help with logistics and intelligence gathering, as well as recently taking part in airstrikes in Iraq. The Internet video released on Friday begins with a news clip announcing British strikes against the Islamic State group.

British Prime Minister David Cameron said Henning’s apparent slaying showed “how barbaric and repulsive these terrorists are.”

“Alan had gone to Syria to help get aid to people of all faiths in their hour of need,” Mr Cameron said in a statement. “The fact that he was taken hostage when trying to help others and now murdered demonstrates that there are no limits to the depravity of these ... terrorists.”

* Associated Press