The killing of a right-wing activist on the sidelines of an event held by the left-wing party France Unbowed (LFI) in Lyon was inflaming political tensions on Wednesday.
Prosecutors told dpa that 11 suspects have now been taken into custody in a wave of arrests.
LFI lawmaker Raphaël Arnault said that among them was one of his parliamentary assistants and that the employee’s contract will be terminated.
Media reports later said a second assistant to Arnault had also been arrested in connection with the case and had allegedly been working in the French parliament in Paris under a false name.
The developments are putting LFI under increasing pressure.
Conservative and right-wing politicians have suggested that a far-left group of thugs with links to the party beat the activist to death on the sidelines of a right-wing rally protesting an appearance by LFI Member of the European Parliament Rima Hassan in Lyon last week.