"The videotape you are talking about is being investigated," a source in the ministry said, commenting on the footage that was posted online by an IS media outlet on Tuesday.
The 13-minute video shows the execution of a man who has been identified as Muhammad Musallam, 19. The IS group claimed that the man was a spy working for the Israeli foreign intelligence agency Mossad. The Israeli defense minister earlier denied this claim.
According to a French official with intelligence ties, the child soldier who shot Musallam was also a French native.
The Islamic State militant group seized large areas of Syria and Iraq in 2014, and proclaimed an Islamic caliphate on the territories under its control.
Due to the group's intensive propaganda on social networking websites, aimed especially young people, IS managed to recruit thousands of people from all around the world.
A July 2014 public opinion poll, which was conducted in France by ICM Research exclusively for Sputnik News Agency, revealed that 26 percent of French youth polled supports the IS movement.
