Beheading may have involved second Briton

Mr Kassig was captured by Islamic State fighters – also known as IS and Isil – in Syria in October last year while providing medical training and humanitarian aid to victims of the country’s conflict.

Footage of his death, broadcast temporarily on YouTube at the weekend, features an IS fighter speaking with a London accent. He is thought to be Jihadi John, the man apparently responsible for previous hostage killings.

Another Briton, Nasser Muthana from Cardiff, is also thought to be among the killing squad.

His father, Ahmed, said he was shown a still image from the video which pictured a man who “resembled” his son. Nasser and his brother Aseel fled the UK in June to fight for IS in Syria.

Asked how certain Mr Muthana was that Nasser was among those in the latest video, he said: “Not quite sure.

“It resembles him. I was shown a picture of the video. I cannot confirm it is him, but I think it might be.”

The video also shows what the terrorists claim is a group of at least 10 Syrian pilots being murdered by militants.

Prime Minister David Cameron condemned IS as a “depraved organisation”. He will convene a meeting of the Government’s Cobra contingency committee to consult with security chiefs and other senior officials about the latest developments, Downing Street said.

Mr Kassig’s parents said their son died “as a result of his love for the Syrian people”.

The American aid worker was born Peter but changed his name to Abdul-Rahman following his conversion to Islam while in captivity.

Mr Cameron said: “These beheadings show once again what a depraved organisation this is.

“Like others who have been murdered in cold blood by Isil, Abdul-Rahman Kassig was a selfless humanitarian worker who had gone to the region to help care for those fleeing the Syrian conflict.”

US President Barack Obama praised Mr Kassig as a “humanitarian” who “cared deeply about the plight of the Syrian people”.

He said: “Abdul-Rahman was taken from us in an act of pure evil by a terrorist group that the world rightly associates with inhumanity.”

He added: “His life and deeds stand in stark contrast to everything that Isil represents. While Isil revels in the slaughter of innocents, including Muslims, and is bent only on sowing death and destruction, Abdul-Rahman was a humanitarian who worked to save the lives of Syrians injured and dispossessed by the Syrian conflict.”

Previous beheading videos showed a desert landscape but in this latest release the IS militant appears to be standing in front of a town with fields in the distance.

Speaking before the video emerged, Mr Cameron said he wants Jihadi John to face justice, after reports that he was injured in an allied air strike against IS commanders in Iraq.

The masked fanatic, believed to be responsible for the beheading of two British and two US hostages, is reported to have been taken to hospital after narrowly escaping death in the raid. He has become one of the world’s most wanted after the first beheading footage – the killing of US journalist James Foley – was broadcast on August 19.