The terrorist group ISIS has released another graphic video purporting to show the beheading of a British aid worker taken hostage in Syria.

The short video, which we're not airing due to its graphic content, shows 44-year-old David Haines in an orange jumpsuit kneeling beside a black-clad militant. The militant is shown executing Haines, then threatening the life of another British hostage.

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The executioner, speaking in a British accent similar to one featured in two other ISIS videos that show the beheading of Westerners, claims Haines was killed in retaliation for U.K. Prime Minister David Cameron's support of the Kurdish Peshmerga's campaign against the terrorist group. The second hostage is reportedly also a captured aid worker.

A dedicated humanitarian worker and father of two, Haines has previously worked for aid agencies in Libya and South Sudan. He was abducted in Syria in March 2013 while working for the nonprofit group ACTED.

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Haines' life was threatened by ISIS in their previous video, which showed the execution of American journalist Steven Sotloff, who was beheaded in a similar manner after falling into the hands of the group.

The execution video was released one day after Haines' family issued a public plea to ISIS urging the militants to contact the family, presumably to negotiate his release.

It's the third such execution video ISIS has released targeting Western media — but the first video to show the death of a British national. A CNN analyst predicts the execution could inspire the U.K. to take a larger role in the international campaign to destroy ISIS.

"I think this will galvanize the British population. This is pushing the British over the fence, and I cannot believe ISIS didn't factor that in."

Cameron responded to the video on Twitter Saturday, calling the execution an act of "pure evil" and vowing to bring the murderers to justice.