France has confirmed that a second Frenchman features in a video showing the beheading of Syrian prisoners, and the body of a US hostage killed by Islamic State (IS).
French media quote unnamed official sources as saying he is a 22-year-old from an eastern suburb of Paris.
Earlier, the government named Maxime Hauchard, from Normandy, as a militant in the video released at the weekend.
About 1,000 French jihadists are thought to have gone to Syria and Iraq.
On a visit to Australia, French President Francois Hollande told reporters in Canberra that “there were two French people” in the video.
“One has been categorically identified and the other one is in the process of being identified,” he said.
An official in the Paris prosecutor’s office, Agnes Thibault-Lecuivre, said there was a “strong presumption” that Michael Dos Santos, a 22-year-old from Paris’s Champigny-sur-Marne suburb, was in the video, AP news agency reported.
French broadcaster France 2 said (in French) that Mr Dos Santos had also been identified by a friend, who said the man had surprised his family when he suddenly converted to Islam.
Mr Hollande said officials had not established the “exact role” of the two militants.
He called for families to be given more information about the danger of jihadist websites and urged families to be “vigilant” in stopping young people from being recruited by extremists.
In the latest IS video – unlike previous ones showing beheadings – several militants appear with their heads uncovered.
Earlier this week, Mr Hauchard was named by a French prosecutor as one of those leading Syrian prisoners to their execution.
The video also shows the severed head of Abdul-Rahman Kassig, a US aid worker who was kidnapped in Syria last year.