Islamic State militants released a video purporting to show the beheading of British hostage, aid worker Alan Henning, Friday.

The footage on YouTube showing a bearded man in an orange jumpsuit kneeling next to a black-clad man was similar to past Islamic State beheading videos of two Americans and a Briton.

The one-minute video, titled Another Message to America and its Allies, showed Henning say "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".

Alan Henning, a Salford taxi driver, was delivering aid to Syria last December when he was kidnapped then held hostage by the Islamic State, the BBC reports.

IS had threatened to kill the 47-year-old in a video showing the killing of Briton David Haines last month.

British prime minister David Cameron said in a statement that the apparent murder showed "just how barbaric and repulsive these terrorists are". Cameron stressed that Britain would do all it could "to hunt down these murderers and bring them to justice".

"The United States strongly condemns the brutal murder of United Kingdom citizen Alan Henning," President Barack Obama said in a statement.

"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," Obama said, referring to other captives killed by Islamic State militants.

Near the end of the video, another hostage identified as American Peter Edward Kassig is introduced. His parents later issued a statement saying their 26-year-old son had been taken captive while doing humanitarian work in Syria.

Islamic State is believed to be holding fewer than 10 Western hostages in Syria including British journalist John Cantlie, who has appeared in three Islamic State videos.

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