The mother of Mohammed Emwazi knew instantly he was Jihadi John when he first appeared in front of the cameras in the murder of American journalist James Foley after recognising his voice, Kuwaiti investigators have been told.

Ghania Emwazi screamed "that's my son" as she view last August's footage of the knife-wielding executioner making a speech in English while standing behind Mr Foley moments before beheading him.

But she did not tell the authorities, it is believed.

Mr Foley, 40, was the first of at least five Western hostages of the ISIS thought to have been executed at the hands of Mohammed Emzawi, who grew up in London.

But it emerged on Monday that Emwazi's parents had been aware of their son's activities for months after realising that his was the voice on the video, according to testimony given to Kuwaiti police by his father, Jassem, 51.