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 Islamic State 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.

Since the 2012 killings in Toulouse, Jews have been targeted by French extremists twice. Four died in a kosher supermarket during three days of terror in the Paris area this year that left 20 people dead, including the three gunmen, and a French ex-fighter for Islamic State is also charged in a deadly attack on a Jewish museum in Brussels.

But the boy seen in the video Tuesday, who appears to be a young adolescent, and the death announced earlier this week of the French teen appeared to mark a new emphasis on foreign children.

"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.

White House spokesman Josh Earnest called the killing an "abhorrent and unjustifiable action," adding that the compelling of a child to kill further demonstrated the Islamic State group's "disregard for all human decency." Yet he noted the video comes amid signs of dissent within IS ranks and reports of IS fighters being executed while trying to flee and defect, suggesting the group was flailing under increased pressure.

"That is an indication that we're continuing to apply pressure to ISIL in a way that is actually succeeding in degrading their ability to wreak havoc in that part of the world," Earnest said, using another acronym for the militant group.

The father of the Palestinian killed said that his son was no Israeli spy but was tricked into joining the militants and then regretted his decision. Said Musalam said IS lured his 19-year-old son Mohamed with promises of women, money and cars.

"They promised a lot of things and then I came here and there is nothing," Musalam recalled his son saying in a phone call to his East Jerusalem home from Syria.

The son said he was in Raqqa, the de-facto capital of the Islamic State group, and had heard his mother was sick and wanted to come back, the father added.

Musalam told the AP that his son left for Syria four months ago without telling his family and later told his brother that he was going to fight with IS. More than a month ago, the family received a call from an unidentified person who said Musalam had fled IS, was caught at a Turkish checkpoint, and was put in IS jail.

"They did not want to let him leave because if he comes back, he might be caught by the Israelis and tell them what he had seen. So they wanted to get rid of him," the father said. "I know my son. I raised him well. I am sure he's not working for the Mossad."

Musalam said he wished his son's fate upon the family of Islamic State group's leader Abu Bakr al-Baghdadi.

"I will leave it to God and what happened to my son Mohamed I hope God will do the same for you, your sons and your family," Musalam said in Arabic, addressing al-Baghdadi. "God knows that one day we'll meet, whether in paradise or in hell, and we'll settle the accounts."

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. Abu Bakr al-Firansi was killed two months ago, the official said, describing 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. Since the Jan. 7-9 attacks in the Paris region, France has deployed tens of thousands of security forces to protect religious, tourist and travel sites -- measures the government said Wednesday would be extended until at least early summer.

"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."