A young woman was beaten up by a gang of girls as she sunbathed in a park wearing a bikini.
It is thought the five attackers objected to their victim being immodestly dressed in public.
They pulled her hair, punched her and slapped her around the face, leaving her badly bruised.
The incident, which has prompted outcry on social media, took place as the 21-year-old victim, Angelique Slosse, lay in the sun with two friends in a park in the French city of Reims, north of Paris.
As the gang walked by, words were exchanged. At one stage one of the attackers was heard to say: "Go and get dressed."
Another verbally abused her for "immorally" exposing so much bare flesh in a public place. Miss Slosse replied to their comments and was attacked. She suffered severe bruising and has not been able to go to work since the incident last Wednesday.
The five attackers, aged between 16 and 24, were arrested.
Police said the victim was not able to tell them whether her attackers were motivated by religious views.
Last night the local police superintendent, Julie Galisson, said: "It was a fight between young girls which degenerated after one of the authors of the aggression said, 'Get dressed, it's not summer'."
One of those arrested would not leave Miss Slosse alone and this degenerated into violence, Mrs Galisson said.
She added: "As is clear from the statement of the victim and those implicated, there is no religious or moral element which explains the aggression."
However the incident has caused outrage in France, where it is seen as the latest threat to French values by hardline Islamists. A dozen bikini-wearing women organised a protest in the park, braving rain and cold winds.
Hundreds of others responded to a Twitter appeal by the French anti-racist organisation SOS Racisme, posting images to show they supported the wearing of bikinis in public. They were asked to use the hashtag #jeportemonmaillotauparc (I wear my swimsuit in the park).
One large group posted a picture of themselves in bikinis with the comment: "All women are free in their bodies, and no one can decide for them."
The protests echo the Je Suis Charlie campaign that went viral on social media in January following the massacre of 12 people by Islamic extremists at the Paris offices of satirical magazine Charlie Hebdo.
The mayor of Reims, Arnaud Robinet, said that what had happened was an "intolerable aggression" but added: "We have to be very careful not to jump to conclusions. All the same, I can understand why people have assumed that this attack had religious motives. If that turns out to be the case it is a very serious incident."
- Daily Mail