France's president has called Tuesday's fatal shooting of a teen by police "unforgivable", saying "nothing justifies" a young person's death.
Emmanuel Macron's comments come after protests over the killing gripped the Paris region overnight.
Nahel, aged 17, was shot in his car after failing to stop when ordered to.
But the president's comments prompted an angry reaction from police unions, who accused him of rushing to judge the officers involved.
The Alliance Police union called for them to be presumed innocent until found guilty, while the rival Unité SGP Police also spoke of political interventions that encouraged "anti-cop hatred".
Interior Minister Gérald Darmanin said he would be taking legal action against another group, France Police after it published what he called an "unacceptable and abject" tweet seeking to justify the teenager's killing.
Prime Minister Élisabeth Borne also weighed in, saying the police intervention "manifestly did not conform to the rules".
Video of the incident on social media shows an officer pointing a gun at the driver of a car before a gunshot is heard and the car then crashes to a stop.
The teenager died of bullet wounds in the chest, despite help from emergency services.
The officer accused of shooting him, who said he had fired because he felt his life was in danger, is in custody on charges of voluntary manslaughter.
A series of protests followed the shooting on Tuesday night in Nanterre, the area just west of Paris where the teenager was killed. Some 31 people were arrested following the disorder.
PHOTO/AFP
Cars and rubbish bins were set alight and bus shelters were destroyed. Fireworks were also set off near the police station. Riot police used tear gas to break up protesters, some of whom had set up barricades.
Nahel is the second person this year in France to have been killed in a police shooting during a traffic stop. Last year, a record 13 people died in this way.
According to French media, police initially suggested the teen drove his car towards them with the intention of hurting them.
But footage posted online and verified by the AFP news agency shows an officer pointing his weapon at the driver through his window and appearing to fire at point-blank range as he tries to drive off.
The agency also reports that a person in the video can be heard saying, "You're going to be shot in the head" - but it is unclear who says it.
Two others were in the car at the time of the shooting. One fled while another, also a minor, was arrested and held by police.
"Nothing justifies the death of a young person," President Macron told reporters in Marseille, calling for "calm for justice to be done".
"I would like to express the feelings of the entire nation at what has happened and the death of young Nahel, and to tell his family of our solidarity and the nation's affection."
"We have a teenager who has been killed. It's inexplicable, unforgivable," he said, adding that the case was immediately referred to the courts where he hoped justice would "do its job quickly".
The president's remarks are meant to calm a potentially inflammable atmosphere in Nanterre, near the La Défense business district, and other Paris suburbs, where the killing of Nahel has triggered strong emotions.
In response to fears that Tuesday night's riots could be repeated this evening, the government has announced there will be strong police reinforcements on the streets.
The Nanterre shooting is set to be one of those symbolic moments that define the troubled relations between police and disaffected populations in the suburban cities, or estates.
The government can see this as well as anyone, which is why it will be treading very carefully over the next few days. Gérald Darmanin, the interior minister, set the tone when he said that the police action was - from the look of it - unacceptable.
The danger is that the rioting of Tuesday extends over the coming nights. Hot weather, long evenings and the end of the school term could easily combine with a sense of righteous indignation to push more youths onto the street.
The long nights of suburban rioting in 2005 have not been forgotten.
One gesture that could well be under consideration is a review of rules on gun use by police at checkpoints.
No one disputes that refusing to stop at a traffic control is a serious offence and that it happens too frequently. But on 13 occasions last year, occupants of cars in such situations were shot dead by French police. That strongly suggests something is wrong.
In a video posted on TikTok, Nahel's mother Mounia urged people to join her on a march for her son.
"Come all, I beg you," she said. "We will all be there."
"I'm hurting for my France. An unacceptable situation. All my thoughts go out to Nahel's family and loved ones, this little angel gone far too soon," France and Paris Saint-Germain striker Kylian Mbappé wrote on Twitter.
Authorities have opened two separate investigations following the teen's death - one into a possible killing by a public official, and another into the driver's failure to stop his vehicle and the alleged attempt to kill a police officer.
Paris police chief Laurent Nuñez told French television station BFMTV that the policeman's actions "raise questions", though he suggested the officer may have felt threatened.
The 17-year-old's family lawyer, Yassine Bouzrou, insisted that was an illegitimate defence, telling the same channel the video "clearly showed a policeman killing a young man in cold blood".
He added that the family had filed a complaint against police for "lying".
