French police are continuing an intensive search for a gunman who carried out yesterday's attack outside a Jewish school in Toulouse in which three children and a teacher were killed.

With a grieving nation in shock, French President Nicolas Sarkozy ordered a minute's silence to be observed in all schools this morning and has suspended his re-election campaign until at least tomorrow.

French Interior Minister Claude Gueant admitted that police do not know the identity of the suspect behind three deadly attacks in eight days, but quoted a witness as saying the attacker had worn a video camera.

The minister said thousands of identity checks had already been carried out in a bid to catch the killer, who used the same weapon and stolen scooter in all three attacks.

The killer's first target was a paratrooper of North African origin, shot dead in Toulouse on 11 March.

Four days later the suspect shot dead two more soldiers of North African origin in the nearby garrison town of Montauban, and seriously wounding a soldier from the Caribbean.

French authorities have stepped up security at Jewish and Muslim schools following Monday's assault on the Ozar Hatorah school, and Mr Sarkozy declared a maximum "scarlet" terrorism alert on the Midi-Pyrenees region.

The scarlet alert gives authorities widespread powers to disrupt daily life and implement sweeping security measures, including potentially closing rail terminals and airports or even halting water supplies.

"In attacking children and a Jewish teacher, the anti-Semitic motive of the attack appears to be obvious," Mr Sarkozy said in a nationally televised address after he returned to Paris from the scene of the shooting.

Mr Sarkozy observed the minute's silence at a school in central Paris, before meeting with Jewish and Muslim community leaders.

The bodies of the four Franco-Israeli citizens, three of them young children, who were murdered in the school shooting are to be flown to Israel.

Teacher Jonathan Sandler, his two sons Gabriel, aged four, and Arieh, aged five, and a seven-year-old pupil at the Ozar Hatorah school, Myriam Monsonego, are to be brought to Paris from Toulouse before being put on a plane.

Witnesses said Mr Sandler died trying to shield his sons, and that the gunman had chased Miriam, the daughter of the school head, into the school before shooting her in the head.

Yaacov Monsonego was praying in the school synagogue when another young pupil brought him the body of his daughter.

A fifth victim, a 17-year-old boy, was wounded, but local community leaders said he was expected to survive.

The killer wore a full face helmet and appeared calm and collected, carefully parking his scooter before opening fire, witnesses said.

Police are particularly concerned that the killer might strike again, having stuck three times at precise four day intervals.