Islamic State: British Aid Worker Alan Henning Purportedly Beheaded in Video Released by Militant Group

The Salford taxi driver was delivering aid to Syria in December when he was kidnapped then held hostage by IS.

The one-minute video, titled Another Message to America and its Allies, showed the British aid worker introducing himself, said SITE Intelligence Group, which monitors jihadist groups.

Mr Henning says "because of our parliament's decision to attack the Islamic State, I, as a member of the British public, will now pay the price for that decision," according to SITE.

Dressed in an orange prison-style outfit and on his knees, Mr Henning was filmed with a masked militant standing over him wielding a knife.

The video is almost identical to those released after three previous murders, including those of US journalists James Foley and Steven Sotloff.

British prime minister David Cameron, in a statement released after the video emerged, described the IS militants as "repulsive" and said the apparent murder showed "just how barbaric and repulsive these terrorists are".

US president Barack Obama also condemned the "brutal" murder.

"Standing together with our UK 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," Mr Obama said, referring to other captives killed by Islamic State militants.

The White House and the British Foreign Office are both assessing the video, which the latter said, if authentic, shows a "further disgusting murder".

"We are aware of the video and are working urgently to verify the contents," a spokesman for the British Foreign Office said.

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

Prime Minister Tony Abbott also condemned the militants.

"This is more proof of the importance of the coalition effort against ISIL, more proof that this is a murderous death cult and more proof that ISIL is against God, against Islam and against humanity," he said.

The militant group had threatened to kill Mr Henning in a video showing the killing of UK hostage David Haines released last month.

Mr Henning's wife Barbara had recently appealed to IS to release him, calling her husband "a peaceful, selfless man".

Black-clad jihadi vows to 'strike necks' of Westerners

In the video, the jihadist, who has the same British accent as the killer in the video of the death of Haines, addresses Mr Cameron.

"The blood of David Haines was on your hands, Cameron. Alan Henning will also be slaughtered, but his blood is on the hands of the British parliament," he declares.

The jihadist also addresses Mr Obama.

"Obama, you have started your aerial bombardment in Sham, which keeps on striking our people," the militant says, using the Arabic term for Syria and the Levant.

"So it is only right that we continue to strike the necks of your people."

Shuja Shafi, secretary general of the Muslim Council of Britain, the UK's largest Islamic umbrella group, called the purported beheading of Mr Henning "a despicable and offensive act".

"It is quite clear that the murderers of Alan Henning have no regard for Islam, or for the Muslims around the world who pleaded for his life," he said.

American hostage appears at end of video

Near the end of the video, the militant introduces another hostage identified as American Peter Edward Kassig.

His parents later issued a statement confirming their 26-year-old son had been taken captive while doing humanitarian work in Syria.

"We ask everyone around the world to pray for the Henning family, for our son, and for the release of all innocent people being held hostage in the Middle East and around the globe," Ed and Paula Kassig of Indianapolis, Indiana, said in the statement.

Mr Kassig served in the US Army during the Iraq war before being medically discharged, the family said. Pentagon records show he spent a year in the army as a ranger and was deployed to Iraq from April to July 2007.

After leaving the army, Mr Kassig became an emergency medical technician and travelled to Lebanon in May 2012, volunteering in hospitals and treating Palestinian refugees and those fleeing Syria's nearly four-year civil war, the family added.

He was detained on October 1, 2013, while travelling to the eastern Syrian city of Deir al-Zor while working for Special Emergency Response and Assistance, a non-governmental organisation he founded in late 2012 and based in southern Turkey to treat refugees flowing across the border from Syria, his family said.

While in captivity, he converted to Islam and took the name Abdul Rahman, a family spokeswoman said.

IS is believed to be holding less than 10 Western hostages in Syria. This includes British journalist John Cantlie.

Mr Cantlie's father Paul had earlier urged IS to release his son. He said the family had not known John was alive until he appeared in a recent series of IS videos.