French authorities have launched a manhunt for a suspected serial killer who opened fire at a Jewish school in the southern city of Toulouse, killing a rabbi, his two young sons and the principal's young daughter.

The French government raised its terrorism alert to the highest level for the southwestern region around Toulouse in response to Monday's shooting at the Ozar Hatorah school by a lone gunman who sped away on a motorcycle.

It was the third fatal shooting in the Toulouse area in eight days by a gunman on a motorcycle using the same type of weapon. In the two earlier incidents, an assailant opened fire on French soldiers of North African and French Caribbean origin, killing three of them.

French President Nicolas Sarkozy rushed to the scene of the school attack and said he believes all three shootings were linked by “murderous” racism toward French minorities. He also said “the anti-Semitic motivation” against the Jewish school assault is “obvious.” Authorities quickly increased security at Jewish and Muslim schools and houses of worship across the region.

Witnesses say the gunman, his face disguised by a helmet, stormed into the school just before the start of morning classes and fired at the rabbi and the three children, all under age 10. A 17-year-old boy also was shot and seriously wounded. The attacker's first weapon jammed, prompting him to switch to a second gun.

Mr. Sarkozy called the shooting “a national tragedy” and ordered a moment of silence to be observed in all French schools on Tuesday. He also suspended his re-election campaign until Wednesday. Mr. Sarkozy's main challenger in the May vote, Francois Hollande, also rushed to Toulouse to pay his respects.

The rabbi and three children killed in the attack all were dual French and Israeli citizens. Israeli Prime Minister Benjamin Netanyahu condemned the shooting as a “despicable murder” and said Israel will do everything it can to help French authorities find the killer. His government also said the four victims will be buried in Israel.

In Washington, the White House said it was deeply saddened by the attack and condemns it as an “unprovoked and outrageous act of violence.”