French authorities are investigating claims that a southern town tracks how many Muslim children attend its schools, which would be illegal and run counter to France's secular view of itself.

The claims by the extreme right mayor of Beziers drew attention at the highest levels, reflecting heightened tensions around religion following the terrorist attacks in January.

The prime minister called Tuesday for swift action. Interior Minister Bernard Cazeneuve said counting children by religion "sends us back to the darkest hours of our history," referring to French collaboration with the Nazis. France's laws against counting people by religion or ethnicity stem in part from the Holocaust.

Beziers Mayor Robert Menard claimed on French television Monday night that based on his statistics, more than half the schoolchildren in his town are Muslim.