An 11th person was detained on Sunday,
police said, as authorities investigated the murder of Samuel Paty, a history teacher who was beheaded by a suspected Islamist in an attack that stunned the country.
Satirical magazine Charlie Hebdo, whose offices were attacked in a mass killing five years ago, was among groups organising a tribute to Paty in
Paris in the afternoon.
The 47-year-old teacher was killed on Friday outside his school in a Paris suburb by an 18-year-old attacker.