Islamic State beheads British hostage Henning

British Prime Minister David Cameron on Friday night confirmed the “brutal murder” of aid worker Alan Henning by the Islamic State group and vowed to bring his killers to justice.

“The brutal murder of Alan Henning by ISIL (another term for IS jihadists) shows just how barbaric and repulsive these terrorists are,” Cameron said in a statement released by his Downing Street office.

The White House said that a video showing the execution of British hostage Henning was yet another example of the “brutality” of the Islamic State group.

President Barack Obama’s top counter-terrorism advisor Lisa Monaco called the killing “yet another demonstration of the brutality of ISIL.”

A frame from a video released Friday, Oct. 3, 2014, by Islamic State terrorists that shows the killing of British aid worker Alan Henning (photo credit: AP Photo)

In the video, almost identical to those released after three previous murders, a masked IS militant also displays a hostage he identifies as an American, Peter Kassig.

IS has previously released videos showing the beheadings of American journalists James Foley and Steven Sotloff (who also held Israeli citizenship), and another British aid worker David Haines.

Slain US journalists James Foley, left, and Steven Sotloff, right. Both were executed by the Islamic State jihadist group two weeks apart in late August and September 2014.

The video mirrored other beheading videos shot by the Islamic State group, which now holds territory along the border of Syria and Iraq. It ended with an Islamic State fighter threatening Kassig.

“Obama, you have started your aerial bombardment of Shams (Syria), which keeps on striking our people, so it is only right that we continue to strike the neck of your people,” the masked militant in the video said.

Two US officials, who spoke on condition of anonymity out of concerns of not having permission to release the information, confirmed that Peter Kassig is being held by Islamic State militants. The officials declined to elaborate.

Peter Kassig standing in front of a truck filled with supplies for Syrian refugees. A video produced by militants in Syria released Friday, Oct. 3, 2014, shows Kassig, of Indianapolis, kneeling on the ground as a masked militant says he will be killed next. (photo credit: AP Photo/Courtesy Kassig Family)

Britain has been supporting U.S. military efforts against the Islamic State group by using British forces to help with logistics and intelligence gathering, as well as recently taking part in airstrikes in Iraq. The Internet video released Friday begins with a news clip announcing British strikes against the Islamic State group.

“Alan had gone to Syria to help get aid to people of all faiths in their hour of need,” Cameron said in a statement. “The fact that he was taken hostage when trying to help others and now murdered demonstrates that there are no limits to the depravity of these … terrorists.”

Henning, 47, nicknamed “Gadget,” had joined an aid convoy and was taken captive on Dec. 26, shortly after crossing the border between Turkey and Syria. Earlier this week, Henning’s wife Barbara Henning asked the militants in a televised plea: “Please release him. We need him back home.”

Dozens of Muslim leaders in Britain had urged the Islamic State group to release Henning. His wife had said she had been given hope by “the outcry across the world” over her husband’s imprisonment.

Mohammed Shafiq, chief executive of the Ramadhan Foundation, a Muslim charity, called Henning “a British hero.”

His “barbaric killing is an attack against all decent people around the world,” Shafiq said.

The Islamic State group has its roots in al-Qaida’s Iraqi affiliate but was expelled from the global terror network over its brutal tactics and refusal to obey orders to confine its activities to Iraq. It became even more extreme amid the bloody 3-year civil war in neighboring Syria, growing stronger to the point of being able to launch a lightning offensive across much of northern Iraq, routing security forces there and shooting down an Iraqi helicopter on Friday. The group has become known for filming and releasing footage of mass shootings it conducts, as well as beheading opponents and targeting religious and ethnic minorities in the areas it attacks.

The extremist group has been widely denounced by mainstream Muslim authorities.

Other foreigners are believed held by the Islamic State group. On Friday, the father of John Cantlie, a British photojournalist held by the group, appealed for his release in a video, saying he was a friend of Syria.