The Islamic State group (ISIL) released Saturday a video showing the beheading of the British aid worker David Cawthorne Haines who was taken captive in Syria in March 2013.

The video, apparently showing the gruesome beheading by a masked ISIL executioner believed to be a British citizen, is similar to the execution footages of American journalists James Foley and Steven Sotloff released in recent weeks.

Like Us on Facebook

The British foreign ministry rushed to investigate on the footage and still has not verified its authenticity.

But Prime Minister David Cameron is already condemning Haines's death as "an act of pure evil."

The prime minister vowed to hunt down the Islamic State militants responsible for the death of the British humanitarian worker. Sympathizing with the Haines family who earlier pleaded with the terrorists to communicate with them, Cameron promised to bring the terrorists to justice.

The prime minister called an emergency cabinet meeting yesterday to discuss UK's response.

Another major UK political leader, Ed Miliband of the Labour Party, took to Twitter to denounce the murder as "barbaric" and "disgusting."

Before his capture, Haines was working for ACTED, a French humanitarian aid agency helping the displaced refugees in Syria.

BBC reported that Haines was coordinating the delivery of aid supplies in refugee camps in the Idlib province at the time of his capture.

Speaking to the camera, Haines held the prime minister personally responsible for his death. It is the public, the captive apparently said, that will pay for the anti-ISIL offensive Britain is waging with the United States and its allies.

The Obama administration has issued a statement condemning the murder after the Haines video surfaced yesterday. It promised to stand "shoulder to shoulder" with Britain in its fight against the Islamic State group.

Earlier this month, the United States formed an anti-ISIL coalition to "degrade and destroy" the group that has declared Islamic caliphate across its conquered territories in Syria and Iraq in June. ISIL has been recruiting foreign fighters to join its ranks since.

TagsISIL, beheading video, David Haines