ISIS Appears to Behead British Captive Alan Henning

A video has surfaced online that appears to show the beheading of British captive Alan Henning by a purported member of the terror group ISIS, who then threatens the life of an American aid worker.

"I am Alan Henning. Because of our Parliament's decision to attack the Islamic State [ISIS], I, as a member of the British public, will now pay the price for that decision," Henning says in the video, before his apparent executioner speaks.

"The blood of [fellow slain captive] David Haines was on your hands, [British Prime Minister David] Cameron," the black clad militant says. "Alan Henning will also be slaughtered but his blood is on the hands of the British Parliament."

Henning then appears to be killed. Near the end of the video another hostage, identified as Peter Kassig, is seen alive and kneeling in an orange jumpsuit like the hostages before him.

Kassig, a former Army Ranger and medic from Indianapolis, founded a NGO that did aid work in Syria. He went missing last October.

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Henning's death follows that of Haines, a British aid worker, as well as two American journalists, James Foley and Steven Sotloff, who were all killed separately in a similar, brutal fashion.

Following the latest video's release, Cameron took to Twitter, saying the "brutal murder of Alan Henning by ISIL [ISIS] shows just how barbaric these terrorists are."

In a statement released today, President Obama said the U.S. "strongly condemns" Henning's murder and said his was a "great loss for [the Syrian people], for his family and the people of the United Kingdom."

"Standing together with our U.K. friends and allies, we will work to bring the perpetrators of Alan's murder - as well as the murders of Jim Foley, Steven Sotloff and David Haines - to justice," Obama said.

The British Parliament voted late last week to join coalition airstrikes on ISIS targets in Iraq after Cameron made a passionate plea to lawmakers.

"This is about psychopathic terrorists that are trying to kill us and we do have to realize that, whether we like it or not, they have already declared war on us," Cameron said then. "There isn't a 'walk on by' option. There isn't an option of just hoping this will go away."