Kassig family speaks of 'treasured son'

Kassig's parents Ed and Paula Kassig of the US city of Indianapolis, released a statement on Sunday following reports that their son had become the latest foreign hostage to be murdered by the self-proclaimed 'Islamic State' (IS) group.

"We are aware of the news reports being circulated about our treasured son and are waiting for confirmation from the government as to the authenticity of these reports," they said.

The parents urged the media not to publish or broadcast images released by IS, saying this would be "playing into the hostage-takers hands."

"We prefer our son is written about and remembered for his important work and the love he shared with friends and family, not in the manner the hostage-takers would use to manipulate Americans and further their cause," Kassig's parents added.

'Horrified,' says Cameron

British Prime Minister David Cameron said he was "horrified by the cold-blooded murder."

The US National Security Council (NSC) said in a statement that intelligence authorities were working to confirm the authenticity of the footage. NSC spokeswoman Bernadette Meehan said if it were verified, the White House would be "appalled by the brutal murder of an innocent American."

Soldier turned aid worker

The 26-year-old, born Peter Kassig, took up the first name Abdul-Rahman after converting to Islam following his October 2013 capture, according to friends.

Kassig's family and friends had kept silent for much of the past year, reportedly due to fears for his safety, but made videoed pleas and attended demonstrations calling for his release after Kassig was shown in an October 3 video of the beheading of British hostage Alan Henning.

Delivered aid supplies

Kassig had been delivering aid supplies in eastern Syria when he was taken hostage.

He had served with US military forces in Iraq for four months in 2007 and received an medical discharge later that year.

He later returned to the Middle East as a student of political science, spending time in Beirut.

He left his studies to return to Lebanon in 2012, using his medical skills to treat people who had been hurt in neighboring Syria's war.

Kassig founded an aid organization, Special Emergency Response and Assistance (SERA), delivering supplies and giving medical training to those affected by Syria's conflict throughout the region.

"It's about showing people that we care, that someone is looking out for those who might be overlooked or who have slipped through the cracks in the system for whatever reason," he was quoted as saying in a January 2013 interview with Time magazine.

'Mass beheading' of Syrian military personnel

The same video which claimed the death of Kassig also showed the simultaneous beheadings of at least 18 men, who were described as Syrian military personnel loyal to President Bashar al-Assad. They were described as officers and pilots.

There were substantial differences between Sunday's recording and those released earlier by IS - Kassig was not shown alive in the footage and direct threats were not made towards other Western hostages. Several of the militants' faces were also shown, unmasked.

IS also purported to name the location where the video was filmed – Dabiq, a town in northern Syria.

IS militants have proclaimed a "caliphate" in the territory they control, which spans swathes northern Syria and northwestern Iraq. They govern according to their brutal interpretation of Sharia law.

The United States has led airstrikes against IS in both Iraq and Syria.

se/ipj (AP, dpa, AFP)