Jim Michaels, and Katharine Lackey

USA TODAY

An internet video released Friday appears to show the beheading of a British hostage who had been captured by the Islamic State.

"I am Alan Henning. Because of our Parliament's decision to attack the Islamic State I, as a member of the British public, will now pay the price for that decision," Henning says in the video.

He is wearing an orange jump suit and the video resembles other beheadings carried out by the Islamic State. Officials were in process of trying to authenticate the video, in which a militant also threatens to execute another American hostage.

"Obama, you have started your aerial bombard of Shams (Syria), which keep on striking our people, so it is only right that we strike the next of your people," a masked militant said.

If authenticated, this would be the fourth such video released by the Islamic State. The militants have also released videos showing the beheading of American reporters James Foley and Steven Sotloff and British aid worker David Haines.

The White House issued a statement from Obama late Friday, condemning "the death of Alan Henning."

"The United States strongly condemns the brutal murder of United Kingdom citizen Alan Henning by the terrorist group ISIL," the statement said. "Mr. Henning worked to help improve the lives of the Syrian people and his death is a great loss for them, for his family and the people of the United Kingdom."

Obama added, "Standing together with our UK friends and allies, we will work to bring the perpetrators of Alan's murder – as well as the murders of Jim Foley, Steven Sotloff and David Haines – to justice. Standing together with a broad coalition of allies and partners, we will continue taking decisive action to degrade and ultimately destroy ISIL."

Henning, 47, had joined an aid convoy and was taken captive on Dec. 26, shortly after crossing the border between Turkey and Syria.

In a statement, the British Foreign Office said it was working to verify the video. "If true, this is a further disgusting murder," the statement read. "We are offering the family every support possible; they ask to be left alone at this time."

British Prime Minister David Cameron on Friday said, "The brutal murder of Alan Henning by Islamic State shows just how barbaric and repulsive these terrorists are." He said Henning "had gone to Syria to help get aid to people of all faiths in their hour of need. 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 ISIL terrorists."

Cameron vowed, "We will do all we can to hunt down these murderers and bring them to justice."

A U.S. official, 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 official declined to elaborate.

Henning, 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."

She told the BBC that although some thought her husband was in the wrong place at the wrong time, "He was in the right place doing the right thing." She said her family was "at a loss" as to why Islamic State leaders could not "open their hearts and minds to the truth about Alan's humanitarian motives for going to Syria."

The taxi driver and father of two from Bolton, in northern England, was the only non-Muslim in the convoy, CNN reported.

A video recorded before his capture shows Henning describing his volunteer work in the region. "It's all worthwhile when you see what is needed actually gets where it needs to go," Henning says in the video obtained by CNN.

Dozens of British Muslim leaders in a letter to the Independentlast month had urged the Islamic State to release Henning.

"In Islam, concern for fellow humans and the duty to help everyone is a religious obligation," the letter stated. "Anyone undertaking a humanitarian act is paving his or her way to receive help from heaven."

Muslims were asked to show their support for Henning's cause, as well as that of other Islamic State hostages, by using the hashtag #NotInMyName on Twitter.

Henning's gruesome murder comes after the militant group released a video Sept. 13 showing the apparent beheading of David Haines, another British aid worker. That tape included a warning directed at Cameron. as well as a threat against Henning's life.

Last month, the Islamic State released a chilling propaganda video — the first that doesn't depict a killing — showing British journalist and hostage John Cantlie speaking directly to the camera and promising to reveal the "truth" about the Islamic State.

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 metamorphisized 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.

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

Contributing: Associated Press