A gunman on a motorbike opened fire outside a Jewish school in Toulouse, France, and shot dead three children and a rabbi.
At least three other children were critically injured, including a 17-year-old boy.
The city was said to be on "lockdown" as police hunted the killer, who has also been linked to two recent attacks on soldiers in the region.
It was reported that the same .45 calibre gun was used in the attack as in the two other deadly shootings.
A service to remember the victims was held at a local synagogue and there will be a silent march in Paris later this evening.
The incident occurred at around 8am local time as children waited at a drop-off point near to the Lyceé Ozar Hatorah, which has around 200 students. It is part of a network of more than a dozen institutions which teach more than 4,000 students across France.
"This man alighted from his moped and, as he was outside the school, he shot at everybody who was near him, children or adults. Children were chased right into the school," said Toulouse prosecutor Michel Valet.
Le Monde said that the dead included a rabbi who taught at the school and his two sons. The French newspaper said the man was a French-Israeli from Jerusalem.
Another rabbi, Rahamim Sabag, told Israeli reporters for Channel 2 that the other victim was the headmaster's daughter.
Toulouse prosecutor Michel Valet said: "He shot at everything he could see, children and adults. Some children were chased into the school."
One witness whose child attends the school described "a vision of horror" in the aftermath of the shooting.
French president Nicolas Sarkozy was heading to the scene, as was the French chief rabbi and the interior minister.
Sarkozy said the shootings were an "abominable drama" and a "frightening tragedy".
Declaring a day of mourning, he said schools across France would observe a minute's silence on Tuesday.
The president, who was on the election trail at the time of the shooting but along with the other candidates has suspended his campaign, said: "Whatever happens, faced with this kind of toll, we can say that the French Republic as a whole has been hit by this appalling tragedy."
Maxime Meunier, who is a correspondent for BFM TV, said locals were in a state of "immense shock".
Google Street View shows the school with high levels of security including CCTV cameras, a high metal gate and extended fences.
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The French interior ministry ordered increased surveillance around Jewish schools, and the Minister Claude Gueant said he will visit the school on Monday morning.
The Chief Rabbi of France, Gilles Bernheim, said he was "horrified by what happened this morning in Toulouse". He said that he was "bruised in my body and my soul".
Israel said it was horrified by the shooting, and hoped the French authorities would "shed full light on this tragedy and bring the perpetrators to justice".
Jonathan Hayoun, who leads the Jewish students union of France, said in a statement that "anti-Semitic and racist speech has created a climate of insecurity for Jews in France" and called for new security measures to be put in place.
The shootings come after a week of violent attacks on soldiers of North African origin in the area around Toulouse.
Two French paratroopers were shot in the town of Montauban, near Toulouse, on Friday, when a gunman on a black motorbike pulled up at a cash machine and opened fire.
Police linked those two deaths to another deadly shooting of a soldier in Toulouse, also by an assailant on a scooter, just over a week ago, after ballistics reports said the same gun had been used.
The army called on Saturday for extra vigilance among the soldiers based around Toulouse and called for them to wear civilian clothing.
It is not confirmed if Monday's shootings are linked, but witnesses reported seeing a black motorbike in the area according to Le Monde.
Interior Minister Gueant said there were "similarities" between the attacks.
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Several other attacks on Jewish schools have been recorded in France in previous years.
In 2009 in Marseille aerosol cans soaked in petrol were thrown at a Jewish school, though nobody was injured, and in 2005 acid bottles were thrown at a Jewish school in Paris.