Ahmed Muthana told the Daily Mail newspaper his 20-year-old son Nasser Muthana appeared to be among a group of 16 jihadists who were seen on the video, which also showed the severed head of American hostage Peter Kassig.

"I cannot be certain, but it looks like my son," said Ahmed Muthana, who lives in the Welsh capital city of Cardiff.

"He must fear Allah now for killing people. How can he expect to face Allah if he is killing human beings?"

The announcement of aid worker Kassig's death, the fifth such killing of a Western captive by Islamic State (IS), formed part of the 15-minute video which showed the beheadings of at least 14 men IS said were pilots and officers loyal to Syrian President Bashar al-Assad.

IS, which is fighting in Iraq and Syria, includes thousands of foreign combatants and has become a magnet for jihadi volunteers from Europe and North America, Western intelligence agencies have said.

French Interior Minister Bernard Cazeneuve said there was a strong likelihood that a 22-year-old French citizen also appeared in the beheading video.

The British Foreign office declined to comment.

IS has previously released videos of the beheading of two American and two British men which feature a masked, black-clad militant brandishing a knife and speaking with an English accent, who has been dubbed "Jihadi John" by British media.

Sunday's video showed most of the killers unmasked and the Daily Mail said the man who appeared to be Nasser Muthana was standing alongside Jihadi John.

Nasser Muthana had already appeared in a online video released in June urging Muslims to join IS.

His younger brother Aseel had also travelled to Syria after both were radicalized in Cardiff, his father told the BBC in June. Nasser Muthana's school friend Reyaad Khan also appeared in the online footage in June, various media reports said