A french flag with a "Justice for Quentin" message is displayed as people pay tribute to an activist who died from injuries sustained during a beating on 12 February in Lyon, during a demonstration at Place de la Sorbonne, Paris, France, 15 February 2026; Credit: Reuters/Stephane Mahe

PARIS (Reuters) - Four people, including an aide to a French hard-left lawmaker, have been arrested on suspicion of involvement in the killing of a far-right activist that has jolted the country's political class, a police source said on Tuesday 17 February 2026.

Quentin Deranque, 23, died on Saturday 14 February 2026 after he was beaten to death by hard-left activists outside a conference in Lyon given by Rima Hassan, a far-left member of the European Parliament. Videos of the deadly fight were widely shared on social media.

France Unbowed (LFI) lawmaker Raphael Arnault confirmed on Tuesday that his parliamentary assistant was among those detained, adding that the aide had "stopped all parliamentary work".

"It is now up to the investigation to determine responsibility", he said in a statement on social media platform X.

The aide and three other people have been arrested, said the police source, who spoke on condition of anonymity.

Although conflicts between the hard left and far right are common in France, Deranque's killing has laid bare some of the broader political tensions in a country reeling from nearly two years of institutional crises.

It has also hardened views towards the extreme-left France Unbowed (LFI) party, while allowing the far right to portray itself as a victim of political violence.

Speaking on social media, LFI leader Jean-Luc Mélenchon called for calm. "Let's not fuel the incitement to take the law into one's own hands," he said.

On Monday 16 February 2026, Lyon prosecutor Thierry Dran said a murder probe had been opened into Deranque's killing, which has led to widespread condemnation of the LFI.

Jordan Bardella, party president of the far-right National Rally, said Mélenchon had "opened the doors of the National Assembly to presumed murderers."

After Deranque's killing, French President Emmanuel Macron also appealed for calm.