The death of the 16-year-old, named only as Thomas, has been seized upon by the far-right who has portrayed the killing as symbolic of increasingly insecure conditions in French society.

Olivier Veran, the spokesman of President Emmanuel Macron's centrist government, went to the village of Crepol in southeastern France where Thomas was killed in a bid to keep a lid on tensions.

The death of Thomas is "a tragedy that puts us at risk of a tipping-over of our society, if we don't rise to the occasion," he said.

"It's up to the judiciary to render justice. Not for the French public themselves," he warned, while acknowledging that the death of Thomas was the result of more than a "simple fight at a village dance".

Around 100 extreme-right activists travelled to the nearby town of Romans-sur-Isere on Saturday, a police source said, adding that they were looking for a fight with young people from the La Monnaie neighbourhood, where many suspect the perpetrators of the November 19 killing live.

A further far-right gathering in Romans was dispersed by police Sunday.

- 'Injustice or rage' -

With two dozen people detained over the weekend in connection to these protests, senior prosecutor Laurent de Caigny insisted "no one can take justice into their own hands outside the law" and urged people to allow investigators to do their work.

"Those who oppose this by illegitimate violence will answer for it," he added.

Six of the people arrested at the weekend faced fast-track court hearings on Monday, including for armed attacks on police.

David Riste, headteacher at the boy's school, told pupils after a minute of silence in Thomas's memory that "after such immeasurable pain, a feeling of injustice or even rage can arise".

"We have to trust in our police and our justice system, and stay united in adversity," he added.

One woman in her 70s who had been at the dance told AFP, on condition of anonymity, that whoever was behind the violence should "be punished, and no excuses found for them".

- Tensions running high -

Nine people believed connected to the November 19 violence in Crepol were placed under investigation on Saturday for crimes including murder and attempted murder, prosecutors in nearby city Valence said.

Fighting appears to have broken out inside the dance before spilling outside, with a group of suspects arriving by car as the party was ending.

Conservative and far-right politicians have been swift to point to the fight at the village dance as evidence of danger from immigrants and minorities, even as details of the night's events remain unclear.

Gesturing in the same direction, Interior Minister Gerald Darmanin told security officials and senior police officers Monday that "far-right and far-left groups" should not deter the authorities "from our resolute action" in fighting insecurity.

Prosecutor de Caigny said the violence appears to have broken out for "petty reasons" rather than being a premeditated attack based on "race, ethnicity, nationality or religion" -- perhaps even a passing remark about "somebody's haircut".

But prosecutors have added that nine of the 104 witnesses interviewed reported hearing hostile language "about white people" during the fight.

As well as Thomas's death, nine people were wounded in Crepol on November 19, four of them seriously.

Veran said that victims would be offered legal, psychological and administrative support after meeting one of the injured.

"It's reassuring for locals to know that the state has heard them," Crepol mayor Martine Lagut said.

The Crepol incident came with France already on edge, with a surge in anti-Semitic incidents since Hamas's October 7 attack on Israel and the state's bombing and invasion of the Gaza Strip in response.

Last month's killing of a teacher by a Muslim former pupil originally from Russia has also stoked tensions.