Nine people have been arrested in France following an investigation into the murder of a far-right nationalist student by suspected militants from the far-left.

Those detained include a parliamentary assistant to a deputy from the radical-left France Unbowed (LFI) party.

Quentin Deranque, a 23-year-old maths student, died in hospital on Saturday, two days after being beaten and kicked about the head by a gang of masked young men in Lyon.

It happened after a small demonstration by far-right feminists - who Deranque was supposed to be helping protect - at the city's Institute of Political Studies (IEP), commonly known as Sciences-Po.

The arrests confirm what has widely been reported: that those suspected of the murder are far-left militants linked to a banned group called La Jeune Garde (Young Guard).

The most striking news is that among the nine in custody is Jacques-Elie Favrot, a young man who until now has been employed as parliamentary assistant at the National Assembly in Paris for a deputy from LFI.

The murder is putting huge pressure on LFI, on its 70 MPs, and on its veteran leader Jean-Luc Mélenchon, who is a likely contender in next year's presidential election.

On Sunday, Mélenchon said his party had "nothing to do with this story. Those who accuse us are committing a libel.

"We express our consternation, but also our empathy and compassion for [Deranque's] family and friends. We have said dozens of times that we oppose all forms of violence," he said.

On Monday, state prosecutor Thierry Dran told a news conference that Deranque was kicked and punched by "at least six" individuals, and that the post-mortem examination showed fatal damage to his skull and brain.