Alan Henning
Islamic State has executed British aide worker Alan Henning.SITE/YouTube Screenshot

The ruthless Islamic State militants have beheaded yet another foreign hostage, its fourth such execution in two months.

The hardline Isamlic militants have released the video of the gruesome beheading of British aid worker Alan Henning, who had been marked as the next victim when they executed Briton David Haines last month.

In a one-minute and eleven-second video titled 'Another Message to America and its Allies' released on Friday, the Islamic State showed the execution of 47-year-old Henning in a similar setting and style as seen in the previous executions.

The jihdaist outfit has now threatened to kill an American national, Peter Edward Kassig, next, as per the SITE Intelligence Group, which monitors jihadist activities online.

Henning said in the video that he was "paying the price" for the British parliament's decision to attack the Islamic State.

"I am Alan Henning. 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," he said, minutes before his execution.

Henning's executioner said his "blood is on the hands of the British Parliament".

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

The beheading video surfaced just days after Henning's wife, Barbara, received an audio file from the terror group in which the Briton was heard begging for his life. The Islamic State had threatened to kill the 47-year-old in retaliation to the United Kingdom's continued support to the US in striking Islamic State targets in Iraq.

The brutal killing prompted UK Prime Minister David Cameron to take to Twitter to condemn the act.

"The brutal murder of Alan Henning by ISIL shows just how barbaric these terrorists are. My thoughts are with his wife and their children," he tweeted.

He was also quoted by the BBC vowing to hunt down Henning's "murderers".

"Alan had gone to Syria to help get aid to people of all faiths in their hour of need. 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 ISIL terrorists," Cameron said. "We will do all we can to hunt down these murderers and bring them to justice."

United States President Barack Obama also condemned the latest beheading.

"The United States strongly condemns the brutal murder of United Kingdom citizen Alan Henning by the terrorist group Isil. Henning worked to help improve the lives of the Syrian people and his death is a great loss for them, for his family and the people of the United Kingdom," Obama was quoted saying by the BBC.

Obama also stated that the US and its allies would continue their "action to degrade and destroy ISIL".

"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. Standing together with a broad coalition of allies and partners, we will continue taking decisive action to degrade and ultimately destroy Isil," Obama said.

Henning used to work with a Muslim non-profit organisation in the UK and had travelled to Syria to help refugees, when he was captured by the militants during Christmas last year.

After the executions of American journalists James Foley and Steven Sotloff, and British worker David Haines, Henning was shown to be the next in line as the Islamic State has threatened to kill more foreign nationals in response to the strikes in Iraq and Syria.