Suspected Western Jihadists in 'Evil' IS Beheading Video

Authorities were on Monday investigating the involvement of several suspected Western jihadists in the brutal video by the Islamic State group claiming the beheading of U.S. aid worker Peter Kassig.

The killing of Kassig and the simultaneous beheadings of at least 18 Syrian military personnel in the video sparked global horror, with President Barack Obama calling it "an act of pure evil".

It was the latest in a series of atrocities by IS, a Sunni Muslim extremist group that has seized control of large parts of Iraq and Syria.

The video showed the Syrian men each kneeling on the ground before a separate executioner, whose faces were uncovered.

Among the militants shown beheading the Syrian servicemen were some known foreign fighters, including at least one Frenchman and possibly a Briton, an Australian and a Dane.

French authorities identified at least one of the executioners as believed to be Maxime Hauchard, born in 1992 in northern France and who left for Syria in August last year.

"The video was analyzed by our intelligence services," Interior Minister Bernard Cazeneuve said, adding there was a "strong possibility that a French citizen was directly involved in these despicable crimes."

An intelligence source said it was also being verified whether a second French citizen was among the jihadists seen in the video.

Thousands of foreign fighters have flocked to join IS in Iraq and Syria and experts say they are often among the most violent and brutal of the jihadists.

A British-accented jihadist has been at the center of previous IS beheading videos and appeared again in Sunday's recording claiming Kassig's killing.

Another British jihadist fighting with IS seemed to have appeared as an executioner in the video, his father said.

"I cannot be certain but it looks like my son," the father of Nasser Muthana, a 20-year-old prospective medical student from Cardiff in Wales, told Britain's Daily Mail newspaper.

"He must fear Allah now for killing people. How can he expect to face Allah if he is killing human beings?" added the father, Ahmed Muthana.

Nasser Muthana appeared in an IS recruitment video in June and also boasted about being a "soldier" of the organization on Twitter, according to British media reports. His 17-year-old brother is also reported to have joined him in Syria.

Kassig, who took the name Abdul-Rahman after converting to Islam, was captured last year and was the fifth Western hostage beheaded by IS after two US reporters and two British aid workers.

"Abdul-Rahman was taken from us in an act of pure evil by a terrorist group that the world rightly associates with inhumanity," Obama said in a statement.

In the undated video released on Sunday, the British-accented jihadist stands above a severed head he claims is Kassig's and urges Obama to send more troops to the region to confront IS.

"Here we are burying the first American crusader in Dabiq, eagerly waiting for the remainder of your armies to arrive," the militant says, referring to a northern Syrian town.

Washington is preparing to double its military personnel in Iraq to up to 3,100 as part of the international campaign it is leading against the jihadists.

Kassig, an Iraq war veteran, had risked his life to provide medical treatment and relief supplies to those suffering from Syria's civil war.

Kassig's parents said they were "incredibly proud" of his humanitarian work to help Syrians trapped in a bloody civil war.

"(He) lost his life as a result of his love for the Syrian people and his desire to ease their suffering," Ed and Paula Kassig said in a statement posted on Twitter.

Flags were to be lowered at government buildings in Kassig's home state of Indiana on Monday, Governor Mike Pence said in a statement, calling the killing "an unspeakable act of barbarism".

"Abdul-Rahman Kassig was one of us and he was the best of us. He was... admired by all as a loving son, a dedicated student, an Army Ranger, and a compassionate humanitarian who risked his life to render medical aid to refugees in Syria and Lebanon," Pence said.

Sunday's video was substantially different from previous IS recordings of beheadings. Kassig was not shown alive in the footage, and no direct threats were made against other Western hostages.

The video came as IS suffered battleground setbacks in Iraq backed by U.S.-led air strikes, with government forces Saturday breaking the jihadists' months-long siege of the country's largest oil refinery.

Monitoring group the Syrian Observatory for Human Rights said Monday it had documented the execution of 1,429 people in Syria by IS in the five months since it declared the establishment of a "caliphate" in areas under its control.