France's highest administrative court on Friday suspended a controversial ban on the burkini by a French Riviera town after it was challenged by rights groups.
In a judgement expected to lead to bans being overturned in around 30 towns, the State Council ruled the measure was a "serious and clearly illegal violation of fundamental freedoms".
The court said local authorities could only introduce measures restricting individual freedoms if wearing the Islamic swimsuit on beaches represented a "proven risk" to public order.
The judges said there was no such risk in the case before the court concerning Villeneuve-Loubet, a resort on the Cote d'Azur between Nice and Cannes.
The French Council of the Muslim Faith (CFCM) hailed the ruling as a "victory for common sense".
Police have fined Muslim women for wearing burkinis on beaches in several towns, including in the popular tourist resorts of Nice and Cannes, sparking controversy in France and abroad.
The mayor of one town in Corsica said he would keep his ban in place in defiance of the ruling.
The bans have triggered a fierce debate about women's rights and the French state's strictly-guarded secularism.
- 'Line in the sand' -Amnesty International said the decision had "drawn an important line in the sand".
"French authorities must now drop the pretence that these measures do anything to protect the rights of women," Amnesty's Europe director John Dalhuisen said.
"These bans do nothing to increase public safety but do a lot to promote public humiliation."
CFCM secretary general Abdallah Zekri said: "This victory for common sense will help to take the tension out of a situation which has become very tense for our Muslim compatriots, especially women."
The State Council heard arguments from the Human Rights League and an anti-Islamophobia group (CCIF).
A court in Nice had upheld the Villeneuve-Loubet ban this week.
Anger over the issue was further inflamed this week when photographs in the British media showed police surrounding a woman in a headscarf on a beach in Nice.
The mayor's office denied the woman had been forced to remove clothing, telling AFP she was showing police the swimsuit she was wearing under her top, over a pair of leggings, when the picture was taken.
- 'We are protecting them' -Prime Minister Manuel Valls on Thursday condemned any "stigmatisation" of Muslims, but maintained that the burkini was "a political sign of religious proselytising".
"We are not at war with Islam... the French republic is welcoming (to Muslims), we are protecting them against discrimination," he told BFMTV.
But in a sign of the divisions within the Socialist government on the issue, Education Minister Najat Vallaud-Belkacem said the "proliferation" of burkini bans "was not a welcome development".
Vallaud-Belkacem, who is of Moroccan origin, took issue with the wording of the ban in Nice which linked the measure to last month's jihadist truck attack in the resort that killed 86 people.
"In my opinion, there is nothing to prove that there is a link between the terrorism of Daesh and what a woman wears on a beach," she said, using another term for the Islamic State (IS) group.
- 'No legal justification' -The administrative court in Nice on Monday said the Villeneuve-Loubet ban was "necessary" to prevent "public disorder" after the Nice attack and the murder 12 days later of a Catholic priest by two jihadists in northern France.
But in its ruling, the State Council said: "In the absence of such risks, the emotion and the concerns arising from terrorist attacks, especially the attack in Nice on July 14, are not sufficient to legally justify a ban."
Ange-Pierre Vivoni, the mayor of the small Corsican town of Sisco, said he would keep the ban in place because the issue had sparked a violent beachfront brawl earlier this month.
"I introduced the ban for the safety of property and people in the town because I risked having deaths on my hands," he told AFP.
The vague wording of the prohibitions, which never mention the word burkini, has caused confusion.
Apart from the photographed incident in Nice, a 34-year-old mother of two told AFP on Tuesday she had been fined on the beach in Cannes for wearing leggings, a tunic and a headscarf.
France was the first European country to ban the wearing of the Islamic face veil in public in 2010.