French authorities have arrested 11 suspects over the killing last week of a far-right activist, including an assistant to a hard-left member of parliament, a prosecutor and an informed source said.

Quentin Deranque, 23, died after sustaining a severe brain injury when he was attacked by at least six people last week on the sidelines of a far-right protest against a leftwing politician speaking at a university in the south-eastern city of Lyon.

The incident has fuelled tension between France’s far right and hard left before municipal elections in March and the 2027 presidential race, in which the far-right National Rally (RN) party is seen as having its best chance yet of winning.

The Lyon prosecutor Thierry Dran announced the arrests of nine suspects on Tuesday evening. Two more suspects were arrested on Wednesday, a man suspected of having a direct link to the violence and his partner, who is suspected of having helped him evade justice, Dran said .

An assistant to Raphaël Arnault, a member of parliament from the hard-left France Unbowed (LFI) party, was among those detained, the source said. Arnault reacted by saying he was firing the assistant.

The head of the LFI, Jean-Luc Mélenchon said that those who had attacked Deranque had “dishonoured” themselves by acting with apparent lethal intent. “When it comes to violence, whether it be defensive or offensive … not all blows are allowed,” he said.

An anti-immigration collective called Nemesis, which claims to fight violence against western women, said Deranque had been at the protest in Lyon to protect its members.

Nemesis has blamed the killing on La Jeune Garde (Young Guard), an anti-fascist youth group co-founded by Arnault before he was elected to parliament.

La Jeune Garde – which was dissolved in June – has denied any links to the “tragic events”, while Arnault has called the killing “horrific”.

On Monday, the parliament speaker, Yaël Braun-Pivet, said one of Arnault’s assistants had been banned from the chamber after being mentioned by witnesses.

Thursday’s attack has been described as “a pitched battle between members of the far left and the far right”, according to another source close to the probe.

A video broadcast by TF1 television of the alleged attack shows a dozen people hitting three others lying on the ground, two of whom manage to escape.

A witness told AFP “people were hitting each other with iron bars”.

Lawmakers held a minute of silence on Tuesday afternoon at France’s National Assembly in memory of Deranque, while a march is expected to be held in Lyon next Saturday in his honour.

While the government has singled out the LFI and La Jeune Garde, the Lyon prosecutor on Monday declined to comment on those claims, specifying the incident was being investigated as a voluntary homicide and aggravated assault.

On the far right, the presidential hopeful from the RN, three-time contender Marine Le Pen, condemned the “barbarians responsible for this lynching”.

Jordan Bardella, who heads her party, said after the arrests that the LFI’s Melenchon had “moral and political responsibility” for what happened, claiming he had “opened the doors of the National Assembly to suspected murderers”.

Opinion polls put the far right in the lead for the presidency in 2027, when centrist President Emmanuel Macron will have to step down after the maximum two consecutive terms in office.