A British medical student and a Frenchman who went to Syria last year are believed to be among militants seen unmasked in a video claiming the execution of as U.S. aid worker and Syrian soldiers.
French Interior Minister Bernard Cazeneuve said on November 17 there was a "strong possibility" one of the jihadists is Maxime Hauchard, 22, from Normandy in northern France.
In Britain, Cardiff resident Ahmed Muthana told the "Daily Mail" newspaper his 20-year-old son, Nasser, appeared to be among the jihadists seen in the video.
The graphic video, released by the Islamic State (IS) group on November 16, shows the head of American Abdul-Rahman (Peter) Kassig and the beheadings of at least 18 men described as Syrian soldiers.
Cazeneuve said authorities were analyzing the video and had been investigating Hauchard, who "left to Syria in August 2013 after a stay in Mauritania in 2012."
French citizens make up the largest contingent of European jihadi fighters who have joined extremists in Syria and Iraq.
According to the Paris prosecutor's office, some 1,100 people have been placed under surveillance, and 95 people face charges.
Based on reporting by AFP, AP, and Reuters