TOULOUSE, France — A motorcycle gunman opened fire today in front of a Jewish school here, killing a rabbi, his two small sons and one other child.

It was at least the third deadly motorcycle shooting in France in a week, shocking the country and prompting strong emotions and high-level discussions in Israel. French prosecutors were studying possible terrorist links, but the motive for today’s attack was unclear.

Concerns about a serial killer emerged, as investigators examined whether today’s shooting was linked to two deadly shooting attacks in the Toulouse region last week that killed three French paratroopers and left another seriously injured. French media reported those paratroopers were of Arab origin.

President Nicolas Sarkozy ordered increased security at Jewish and Muslim buildings around Toulouse. His prime minister ordered officials to “secure” all school and religious buildings in France.

France has the largest Jewish community in western Europe, estimated at about 500,000. France also has the largest Muslim population in western Europe, about 5 million.