An adult, his two sons and another child were killed and five other people were injured when a gunman on a scooter opened fire Monday in front of Ozar Hatorah school in a residential area of Toulouse.
Police and local prosecutors said the adult slain was a rabbi who taught Hebrew, his two children, ages 6 and 3, and a 10-year-old child.
City prosecutor Michel Valet said the man "shot at everything he could see, children and adults, and some children were chased into the school" before he fled on the scooter.
Judicial sources confirmed to France 24 that bullets fired at the school were from the same weapon used in two deadly shootings in Montauban and Toulouse. Earlier in the day, officials had stopped short of saying the bullets were fired from the same gun.
On March 11, a soldier was killed near Toulouse, while on Thursday two soldiers were shot to death in Montauban.
Military personnel were ordered not to leave their bases wearing their uniforms.
Police also said Monday they opened an investigation after two synagogues in Paris reported receiving threatening letters, Radio France Internationale reported.
One letter read, "You are the people of Satan. Hell is waiting for you."
One letter was received during the weekend and one was received Monday.
French security officials increased security at Jewish and Muslim schools and religious facilities after the attack.
President Nicolas Sarkozy, who described the killings a "national tragedy," called for a minute of silence Tuesday in schools throughout France.
"These are images which we have seen in other countries which we have never seen in ours," said Sarkozy, who visited Toulouse. "We have no choice but to face it."
Campaigning for France's presidential elections next month was suspended and the candidates, along with other public figures, expressed their horror, shock and sympathy, RFI said. Sarkozy visited the school, followed later by Socialist Party candidate Francois Hollande.
Sarkozy pledged "absolutely everything will be mobilized to find the killer."
Israeli Prime Minister Binyamin Netanyahu called the attack "a loathsome murder of Jews, which included small children."
Netanyahu criticized the United Nations for not condemning the attack while one of its units was to meet a senior Hamas official, The Jerusalem Post reported.
"I haven't heard any condemnation from the U.N., but one of its bodies, the human rights council, invited a representative of Hamas who condemned the US for killing [Osama] bin Laden and kills Jewish men, women, and children," he said of the U.N. Human Rights Council. "I have one thing to say to the UNHRC: What do you have to do with human rights? You should be ashamed of yourself!"
The United States, in a statement issued by National Security Council spokesman Tommy Vietor, also condemned the attack.
"We were deeply saddened to learn of the horrific attack this morning against the teachers and students of a Jewish school in the French city of Toulouse," Vietor said in the statement. "Our thoughts and prayers go out to the families and friends of the victims, and we stand with a community in grief. We join the government of France in condemning this unprovoked and outrageous act of violence in the strongest possible terms."