A second Frenchman was identified on Wednesday after appearing unmasked in a grisly execution video among Islamic State (IS) militants, many of whom are believed to be Western fighters.
As European countries scrambled to identify possible suspects in the execution of 18 Syrian prisoners and US aid worker Peter Kassig, the usually secure Iraqi Kurdish capital of Arbil was hit by a suicide bombing that left four people dead.
There was no immediate claim of responsibility but suicide bombings are usually carried out by Sunni extremists in Iraq, including a series of blasts claimed by the Islamic State militant group in recent weeks.
IS has carried out widespread atrocities since seizing control of large parts of Iraq and Syria, executing five Western hostages and hundreds of locals.
A global outpouring of revulsion met the latest video released by the group on Sunday.
Several of the extremists appeared unmasked in the video and one foreigner, 22-year-old Maxime Hauchard from Normandy in northern France, was quickly identified by French prosecutors.
He is one of several young French nationals from a middle-class, atheist or Catholic background to have converted to radical Islam and gone to fight in Syria, making a profile of potential extremists nearly impossible to pin down, experts say.
A source close to the French investigation on Wednesday identified a second national as 22-year-old Mickael Dos Santos from an eastern Paris suburb, who goes by the name of Abu Othman.