PARIS (REUTERS) - Twelve million pupils returned to school in France on Monday (Nov 2) for the first time since an Islamist militant beheaded teacher Samuel Paty, who had used cartoons mocking the Prophet Mohammad in a class on freedom of expression.

Schools were holding a minute's silence in honour of Paty at 11 am and teachers reminded pupils of their rights and duties in a "free democracy".

Paty was murdered in a middle-class Paris suburb on the eve of a two-week holiday, which President Emmanuel Macron cast as an attack on French values and the Republic itself.

France is at its highest level of security after further attacks, including in a church in Nice and against a preacher in Lyon, since Paty's killing, deploying thousands of soldiers to protect places of worship and schools.

Prime Minister Jean Castex and his education minister will pay their respects alongside staff at the Le Bois d'Aulne college where Paty taught. The high school is keeping its doors closed to students until Tuesday.

Macron has described Paty as a "quiet hero" dedicated to instilling core French values of freedom of belief and expression in his students.

Paty became "the face of the Republic, of our desire to break the will of the terrorists ... and to live as a community of free citizens in our country," the president said in an Oct 21 televised ceremony at Paris' Sorbonne university.

Teachers across France will also read a letter written to teachers by Jean Jaures in which the 19th century political figure sets out their role in nurturing young citizens.

"They will be citizens and they must know what a free democracy is, what rights confers on them, what duties the sovereignty of the nation imposes on them," Jaures wrote.