British aid worker David Haines speaks to the camera before being beheaded. Inset: British hostage Alan Henning, who has been threatened to be next victim.

LONDON : Prime Minister David Cameron vowed Sunday that Britain would hunt down the killers of an aid worker beheaded by the Islamic State, which he described as the “embodiment of evil.”

Cameron said Britain was prepared to “take whatever steps are necessary” after David Haines became the third Western hostage to be beheaded by the militants in less than a month.

IS released a video Saturday showing Haines’ killing and a death threat against another British captive, Alan Henning.

President Barack Obama offered US support for its “ally in grief.”

A grim-faced Cameron said in a televised statement: “We will hunt down those responsible and bring them to justice, no matter how long it takes.

“Step by step we must drive back, dismantle and ultimately destroy ISIL (IS) and what is stands for. We will do so in a calm, deliberate way but with an iron determination.

“We will not do so on our own, but by working closely with our allies, not just the United States and in Europe, but with our allies in the region.”

Cameron is facing growing pressure at home to take military action against IS, but he made no commitment to joining the United States in launching airstrikes on the group in northern Iraq and Syria.

Haines, 44, who was taken hostage in Syria last year, had previously been shown alive in the video of Sotloff’s killing.

The video opens with a clip of Cameron outlining how Britain was working with the Iraqi government to help arm Kurdish fighters against “these brutal extremist militants,” and to offer aid, diplomacy, and military help to pressure IS.

Haines then appears, looking gaunt and dressed in an orange jumpsuit, and identifies himself, before calmly explaining that he is paying the price for Cameron’s policy.

The attacker — who appears to be the same man as in the previous two beheading videos — tells Britain the alliance with the US will “accelerate your destruction” and will drag the British people into “another bloody and unwinnable war.”

At the end of the clip, the militant threatens to execute another British captive, Alan Henning.

Haines’s Croatian wife Dragana was keeping a low profile at their home in the quiet Croatian town of Sisak. They have a four-year-old daughter, Athea, while Haines has a teenage daughter from his first marriage to his childhood sweetheart in Britain. The humanitarian aid group that employed Haines, stressed the “barbaric crime” should not go unpunished.

 
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