A video purporting to show the beheading of American aid worker Peter Kassig by Islamic State fighters was distributed Sunday morning.
The extremist group released a video showing a masked man claiming to have beheaded Kassig and standing over a severed head.
The same video showed the gruesome simultaneous beheadings of at least 18 men described as Syrian military personnel, the latest in a series of mass executions and other atrocities carried out by IS.
“This is Peter Edward Kassig, a US citizen of your country,” said a black-militant wearing a balaclava, the same outfit worn by the man who beheaded two American journalists and two British aid workers in earlier videos.
The man stood over a severed head bearing a resemblance to Kassig, a former American soldier who risked his life to provide medical treatment and aid to those suffering from Syria’s civil war.
In a highly choreographed sequence earlier in the video, jihadists marched at least 18 prisoners said to be Syrian officers and pilots by a wooden box of long military knives, each taking one as they passed, then forced them to kneel in a line and decapitated them.
Kassig, 26, would be the latest Western hostage to be beheaded by the terror group.
The video, which has not been verified, boasts of Kassig’s killing, though it is not actually shown on camera, as opposed to earlier propaganda videos which showed hostages’ beheadings.
The video does not include a threat to execute a new hostage, unlike all previous IS beheading videos.
The White House said that the US intelligence community is working to determine the authenticity of the video.
National Security Council spokeswoman Bernadette Meehan said that if the video is authentic, the White House would be “appalled by the brutal murder of an innocent American,” adding that the White House expresses its deepest condolences to Kassig’s family and friends.
The video emerged just minutes after President Barack Obama departed Australia for the US The president was in Australia for the Group of 20 economic summit.
In an October 3 video showing British aid worker Alan Henning’s beheading, the threat was made that Kassig, who converted to Islam and took on the name Abdel Rahman, would be next.
The group says its brutal executions are in retaliation for US-led airstrikes targeting jihadists in Syria and Iraq.
Before travelling to rebel-held areas in Syria, Kassig worked in hospitals and clinics treating Syrians forced to flee their war-torn country to neighboring Lebanon and Turkey.
He made two separate trips into rebel-held areas of Syria before traveling to the eastern province of Deir Ezzor in autumn 2013, when he was taken hostage.
Kassig’s family and friends had pleaded for his release; his parents released a video in May asking for him to be freed and friends held a press conference in Lebanon earlier this month calling for Islamic State to show mercy.
Kassig “was a very enthusiastic young man, so much that he would help refugees out of his own pocket,” Firas Agha, a Syrian refugee living in Tripoli who shared a flat with Kassig when he lived and worked in the northern Lebanese coastal city, told the news conference.
The former US soldier left the army after fighting in Iraq.
The video includes an appearance by a British jihadist seen in previous videos beheading hostages.
A report late Saturday in the Daily Mail claimed that the Islamic State terrorist, known as “Jihadi John,” was injured in the US-led strike last Saturday that wounded the organization’s leader, according to reports that reached the UK’s Foreign Office.
The jihadist organization triggered global outrage when it released videos of a man with a British accent killing first James Foley, then Steven Sotloff, both freelance journalists who were kidnapped in Syria. The same man then murdered British aid workers David Haines and Alan Henning.
The group is known to have at least one more Western hostage, John Cantlie, who has worked for a variety of British publications and was captured in Syria in late 2012. He has appeared in several propaganda videos released by the Islamic State group.
In addition to murdering the hostages, the Islamic State group has seized a large tract of territory spanning eastern Syria and northwestern Iraq, in a brutal and bloody campaign.
In September, the FBI announced it had identified Jihadi John, but did not release his real name.
On August 8, President Barack Obama ordered airstrikes against the group in Iraq, and this week expanded the campaign — backed by Arab allies — to hit IS targets across the border in Syria.
US authorities expect a long conflict against the group of at least three years, and have expressed concerns that hundreds of Muslims from Europe or the Americas have joined the group.
There are fears in Western capitals that battle-hardened fighters may return from the field and launch attacks in their home countries.
AP contributed to this report.