French President Emmanuel Macron has called for calm ahead of nationwide rallies planned in memory of a far-right activist killed last week.
The marches are for Quentin Deranque, 23, who was beaten to death in a fight that was caught on camera and shocked the nation.
Police are concerned the marches could turn violent, with clashes between opposing extremist political groups.
Mr Macron said his government would hold a meeting to discuss "violent action groups" in the wake of the killing, which has ignited tensions between the left and right ahead of the 2027 presidential vote.
Mr Deranque died from head injuries after being attacked by at least six people on the sidelines of a demonstration against a politician from the left-wing France Unbowed (LFI) party in the southeastern city of Lyon last week.
Speaking at a farming trade fair in Paris, Mr Macron urged "everyone to remain" calm ahead of the rally for Mr Deranque in Lyon, which is set to go ahead under high security despite Lyon's left-wing green mayor asking the state to ban it.
The rally is expected to be attended by 2,000 to 3,000 people, and likely to see counter-protesters from the hard left.
"In the Republic, no violence is legitimate," said Mr Macron, who will be unable to contest next year's election after hitting the two-term limit. "There is no place for militias, no matter where they come from."
Having urged both the far right and hard left to clean up their acts, the president said his administration would hold a meeting next week "take stock of violent action groups which are active and have links with political parties of any description".
Mr Deranque's death has provoked a reaction from US President Donald Trump's administration, with state department official Sarah Rogers yesterday branding the killing "terrorism" and claiming that "violent radical leftism is on the rise".
Likewise, Italian Prime Minister Giorgia Meloni on Wednesday called Mr Deranque's death "a wound for all Europe", prompting Mr Macron to urge the far-right leader to stay out of French matters.
Six men suspected of involvement in the fatal assault have been charged over the killing, while a parliamentary assistant to a radical left-wing MP has also been charged with complicity.
A far-right collective called Nemesis, which claims to "defend Western women" from the violence allegedly wrought by immigrants, said Mr Deranque had been at the protest in Lyon to protect its members when he was assaulted by "anti-fascist" activists.
