Paris Chief Prosecutor Francois Molins on Tuesday warned that the killer who shot dead four people in a Jewish school in southwestern France is "likely to take action again."

The scene of shooting accident is seen in Toulouse, France, on March 19, 2012. Three children and an adult were killed in a shooting outside a Jewish school in the southwestern French city of Toulouse on Monday morning, local media reported, raising the toll up from three. [Xinhua]

"We are facing an extremely determined individual," Molins told a press conference, affirming that the shooting in Toulouse and Montauban was "premeditated".

He said the shooter knew that he is under hunting and warned that he is likely to strike again. The prosecutor also confirmed that the weapon he used to fire at Monday's school attack site was exactly the same one used in similar shootings on March 11 and 15, which left three French soldiers of ethnic minorities dead in Toulouse and Montauban.

A 30-year-old teacher, Jonathan Sandler and his two sons, Gabriel and Arie, and seven-year-old Myriam Monsonego, the daughter of the Ozar Hathora school principal were all shot dead by a gunman on the scooter Monday morning when they were going to class.

The assailant fled on a motorcycle, and the whereabout of the unidentified killer remains unknown and no obvious clues have been found yet.

The prosecutor declared that more than 200 investigators have been mobilized to track down the killer.

French President Nicolas Sarkozy Monday night raised the terror alert to the highest level in southwestern France and vowed to do everything to find the gunman.