BEIRUT (AFP) - Authorities were on Monday investigating the suspected involvement of Western extremists in the brutal video by the Islamic State in Iraq and Syria (ISIS) group claiming the beheading of US 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 US President Barack Obama calling it "an act of pure evil".
It was the latest in a series of atrocities by ISIS, a Sunni Muslim extremist group that has seized control of large parts of both those countries.
The video showed the Syrian men kneeling on the ground each 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 one of the executioners as Maxime Hauchard, a 22-year-old from a small village in Normandy in northern France who left for Syria in August last year.
An image grab made on November 17, 2014 and taken from a propaganda video released on November 16, 2014 by al-Furqan Media allegedly shows members of the ISIS extremist group, with among them a jihadist believed to be French citizen Maxime Hauchard (R), also known as Abu Abdallah al-Faransi, before taking part in the beheadings of at least 18 men described as Syrian military personnel. French Interior Minister Bernard Cazeneuve said on November 17, 2014 "The video was analysed by our intelligence services", adding there was a "strong possibility that a French citizen was directly involved in these despicable crimes". -- PHOTO: AFP
The Paris prosecutor's office said "circumstantial evidence confirms the involvement of a Frenchman in the decapitation of Syrian prisoners shown in an ISIS video released on Sunday."
An investigation into Hauchard was opened in August by French authorities "for criminal association in relation to a terrorist organisation", a judicial source said.
Interviewed in July by French TV station BFM via Skype, Hauchard said he had decided to join IS after watching videos online.
"The personal objective of everyone here is (to become a) shahid (martyr). That is the greatest reward," he said.
An intelligence source said it was also being verified whether a second French citizen was among the extremists seen in the video.
Thousands of foreign fighters have flocked to join ISIS in Iraq and Syria, and experts say they are often among the most violent and brutal of the militants.
A British-accented man has been at the centre of previous ISIS beheading videos and appeared again in Sunday's recording claiming Kassig's killing.
The father of another British recruit fighting with ISIS initially told the media he had also seen his son in the video, but later said he was mistaken.
Britain's Foreign Office refused to comment on speculation about the identity of the fighters in the video, but a spokesman said: "We are analysing its contents."
Kassig, who took the name Abdul-Rahman after converting to Islam, was captured last year and became the fifth Western hostage beheaded by ISIS 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 extremist stands above a severed head he claims is Kassig's and urges Obama to send more troops to the region to confront ISIS.
"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. His 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".
Sunday's video was substantially different from previous ISIS 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 ISIS suffered battleground setbacks in Iraq backed by US-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.