by Charlotte Plantive

French authorities on Tuesday arrested four 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 left-wing politician speaking at a university in the southeastern city of Lyon.

The incident has fuelled tension between France's far right and hard left ahead of 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 at winning the top job.

Lyon prosecutor Thierry Dran said four suspects had been arrested. 

A source following the case, speaking on condition of anonymity, said an assistant to Raphael Arnault, a member of parliament from the hard-left France Unbowed (LFI) party, was among those detained.

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

Placing blame

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 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, only specifying the incident was being investigated as a voluntary homicide and aggravated assault.

LFI's veteran leader Jean-Luc Melenchon, a three-time presidential candidate widely expected to run again next year, has denied his party were to blame.

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

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.