A man and a boy featured in a chilling Islamic State propaganda video showing the killing of a Palestinian have been identified as French citizens, and investigators are looking into whether the man is related to an extremist who attacked a Jewish school in southern France in 2012, an official told The Associated Press on Wednesday.

The official, who has close ties to intelligence services but was not authorized to speak publicly about the inquiry, also said another French fighter whose death was announced this week by Islamic State is a young teenager.

The man in the video, released late Tuesday, speaks with a southern French accent and investigators are probing if he could be the step-brother of Mohammed Merah, who killed seven people in attacks on a Jewish school and paratroopers in the south of France beginning on March 11, 2012 — exactly three years ago.

In photos from Merah's funeral after his death in a shootout with police, the step-brother is identified as Sabri Essid, whose father was married to Merah's mother. Essid strongly resembles the man in the IS propaganda video, notably in the shape of the eyes.

In the video, the man praises attacks on Jews "in your own stronghold in France" as he and the boy stand behind the man about to be killed.

In addition to the 2012 killings in Toulouse, Jews in a kosher supermarket were among the targets of three days of terror in the Paris area this year that left 20 people dead, including the three gunmen.

"Here are the young lions of the caliphate," the man says in the video. Soon afterward, the child is shown shooting the man in the head.

French government spokesman Stephane Le Foll described the video as a "dreadful" killing, but refused to comment Wednesday on the nationalities or identities of the man and boy.

The French official with intelligence ties also confirmed the nationality of a French fighter whose death was announced this week by the Islamic State group. The group said Abu Bakr al-Firansi died two months ago in unclear circumstances. The French official described him as a young teen. According to Europe 1 radio, the child's entire family left last year from the city of Strasbourg to recover the remains of an older brother in Syria, and a second older brother was also killed in the war zone.

About 1,400 people, including entire families, have left France to join extremists in Syria and Iraq, and many have returned. Security officials fear some will arrive with honed skills as fighters, and with passports that allow free travel.

"Nearly 90 French citizens have died there, weapons in hand to fight against our values," French Prime Minister Manuel Valls told France's iTele on Sunday.

About 3,000 Europeans are part of the fight, Valls said, adding: "There could be 5,000 before the summer and without a doubt 10,000 by the end of the year."