(BBC) - A French court has ordered Twitter to hand over details of users who spread anti-Semitic messages, months after offensive tweets were removed.
The Paris high court issued the order to the popular US micro-blogging site at the request of the French Jewish students' union (UEJF) and others.
Anti-Semitism groups hope to identify the users and have them prosecuted.
A spokesperson for Twitter told the BBC News website: "We are currently reviewing the court's decision."
In October, the site agreed to remove French tweets circulating with the hash tag #unbonjuif (#agoodjew) after the UEJF successfully argued that numerous messages had breached French law prohibiting incitement to racial hatred.
The hash tag continued to circulate on Thursday with offensive messages.
Twitter, its spokesperson pointed out, does not monitor content, but reviews reports of content that may be illegal or against its policies, as it comes in.
The court also ordered Twitter to "set up as part of the French platform" an "easily accessible and visible" system that would allow users to alert the site to illegal content which constituted "apology for crimes against humanity and incitement to racial hatred".
he initial court ruling in October came shortly after Twitter shut down an account used by a German neo-Nazi group based in Hanover, at the request of German police.
Twitter used a novel feature called "Country Withheld Content" which means that users in Germany should be unable to see messages posted by the account while they remain visible in other countries.
A French watchdog for anti-Semitic attacks, the SPCJ, recorded a sharp increase last year.
It estimated that crimes ranging from vandalism to murder in the first six months had increased by almost 50%, compared with the same period in 2011.
In March, Islamist gunman Mohamed Merah shot dead a rabbi and three small Jewish children at point-blank range outside a Jewish school in the south-western city of Toulouse.
Earlier this month, the UEJF reported that a new racist hash tag, #sijetaisnazi (#IfIwasaNazi), was trending.
Sacha Reingewirtz, vice-president of the UEJF, welcomed Thursday's court ruling.
"It is a major precedent and breakthrough in the attempt to balance privacy online with the need to combat hate speech," he told the Jewish news website JTA.
Nuno Wahnon Martins, director of European Affairs at Jewish human rights agency B'nai B'rith International, said: "Social networks were created as essentially democratic tools that are also being used by people who oppose democratic principles."
"Like any democracy, the social networks also need to defend themselves, and the first step is to deny those who spread hate speech in anonymity as something to hide behind," he told JTA.
A spate of racist and homophobic tweets followed the anti-Jewish messages, the BBC's Christian Fraser reports from Paris.
One hash tag trending among the most popular in France has been #SiMaFilleRameneUnNoir (#ifmydaughterbroughthomeablackman), our correspondent notes.