The protests against teacher shortages and dilapidated school buildings erupted in the Paris region in September but have turned increasingly violent as they spread nationwide, with dozens injured and police making hundreds of arrests.
"There is an active and violent minority (participating in the protests) ... We're not entirely sure that they are even high school students themselves," Justice Minister Gerald Darmanin told RTL radio on Friday, adding that 2000 people had been arrested since the protests began, with about two-thirds placed in police custody.
"We have gone from high school student demonstrations to a public-order disturbance. When people target buses and set schools on fire, it is no longer simply a protest issue," he said.
In an interview with broadcaster France 2, French Education Minister Edouard Geffray said on Thursday evening that "a little over 400 schools and other educational establishments" would remain closed on Friday.
According to a source close to Prime Minister Sebastien Lecornu, intelligence agencies told a crisis meeting on Thursday that the protest movement had been initiated by politicians from the hard left, including members of La France Insoumise (LFI).
LFI MP Louis Boyard denied the claim in comments to French broadcasters.
Student protesters started fires in at least two high schools on Thursday, while teachers were inadvertently splashed with petrol at a third in the southern city of Marseille, officials said.
At least one car was torched in Strasbourg in the east and riot police clashed with youths in Toulouse in the southwest.
Some high school students in the city of Liege in neighbouring Belgium also began protesting on Thursday.
According to local media, authorities in Liege announced that all schools in the city would close on Friday.
A spokesperson for the municipality did not immediately confirm the closures.
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