CAIRO, Oct. 3 -- The Islamic State (IS) militant group claimed responsibility in an online video on Friday that showed the beheading of British aid worker Alan Henning.

In the one-minute video clip titled "Another Message to America and its Allies," roughly the same as those released after three previous murders, a masked IS militant also introduced another hostage it identified as a U.S. aid worker Peter Kassig.

The video was found online by the SITE private terrorism monitor and opened with a news coverage about the British parliament's vote last week to authorize air strikes against IS targets in Iraq.

The masked militant, who carried out the beheading in the video, has the same British accent as the killer in a previous IS video of the death of British hostage David Haines.

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

He also warned U.S. President Barack Obama, saying that his group will continue to strike "the necks of your people," as the United States has also been carrying out aerial bombardment against his people.

A British Foreign Office spokesman said on Friday that if the video showing the beheading of Alan Henning was genuine, then it was a disgusting murder.

"We are aware of the video and are working urgently to verify the contents," he said, adding that "If true, this is a further disgusting murder. We are offering the family every support possible; they ask to be left alone at this time."

Also on Friday, British Prime Minister David Cameron said the murder of Alan Henning showed the barbarity of IS militants.

"The brutal murder of Alan Henning by ISIL shows just how barbaric and repulsive these terrorists are," he said, adding that "My thoughts and prayers tonight are with Alan's wife Barbara, their children and all those who loved him."

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

In Washington, the White House said the newly released beheading video, the fourth if proven true, is another demonstration of the extremist group's brutality.

Lisa Monaco, U.S. President Barack Obama's counterterrorism adviser, said the United States has seen the latest video, and is evaluating it, adding that the murder is another clear example of why the Obama administration is moving to degrade and destroy the group.

Alan Henning, who was a taxi driver from Salford near Manchester, was held since 2013 by the Islamic State militants. He was on an aid convoy for Syrian refugees when he was captured by the terrorists.

Earlier this week, Henning's wife Barbara pleaded with his captors to free her husband in a video message, in which she said that he was innocent under Islamic Sharia law, and his family needed him.

The extremist militants have already beheaded two U.S. journalists, James Foley and Steven Sotloff, and a British aid worker, David Haines and showed the horrifying process to the world in similar videos on The Internet.