British aid worker David Cawthorne Haines has been beheaded by the Islamic State group (ISIL), according to a video that has circulated Saturday in a website associated with the terrorists, making him the third Westerner and the first British hostage to be executed in recent weeks.

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The ISIL video entitled "a message to the allies of America'' showed the same British executioner in the two previous beheading videos of American journalists James Foley and Steven Sotloff, according to CNN.

Authorities have yet to verify the footage.

The video, reportedly very similar with that of the two previous beheading videos showed David Haines whom the masked man claimed will be killed next, if the United States will not withdraw from its planned anti-ISIL campaign.

Haines's video showed a masked ISIL militant-believed to be the executioner Jihadi John, a UK-born ISIL fighter-standing behind the hostage, who was kneeling in an orange jumpsuit.

The video then showed the gruesome beheading of Haines.

The killer and his hostage, who appeared to be reciting a prepared script, held the British government directly responsible for Haines's death, warning that its alliance with "evil" America will accelerate its destruction and lead its people to a bloody war.

The message personally targeted Prime Minister David Cameron, whom the killer called an obedient lapdog to U.S. President Obama's anti-ISIL policy.

At the end of the footage, the killer was shown placing his hands on another captive whom he identified as Alan Henning, another British citizen, New York Daily News identified as an aid worker for a Muslim NGO.

In a tweet, the PM Cameron condemned Haines's murder as an "act of pure evil," adding that the British government will hunt down the terrorist group and bring the terrorists to justice.

David Haines worked as a logistics and security manager for a French humanitarian group called ACTED. He was abducted in March 2013 in Atmeh, Syria where he worked on aid operations for Syrian refugees.

TagsDavid Cawthorne Haines, David Haines beheading, Steven Sotloff, james foley, ISIS, ISIL, beheading footage