A French court ruled Thursday that Twitter, which has steadfastly refused calls to police its millions of users, must hand over data to help identify the authors of racist or anti-Semitic tweets.
In a test case that pitted the right to free speech against laws banning hate speech, the court granted a request lodged in October by France's Union of Jewish Students (UEJF) which argued that many tweets had breached French law.
The union had been pressing Twitter to exercise tighter control of what appeared on its Internet site following a deluge of anti-Semitic messages posted under the hashtag #unbonjuif (#agoodjew).
Twitter later removed some of the offending tweets.
The UEJF took legal action aimed at forcing Twitter to identify the authors of some of the posts.
The court in Paris on Thursday ruled that the site must do this "within the framework of its French site".
In October, Twitter suspended the account of a neo-Nazi group in Germany following a request from the government in Berlin.
That was the first time that the US firm had applied a policy known as "country-withheld content". which allows it to block an account at the request of state authorities.
Twitter, which last month said the number of active users of the service had topped 200 million, said it deployed the tool developed only last year to restrict content in a single country rather than simply delete posted comments.
German politicians welcomed the step to stop distributing the far-right Besseres Hannover group's "hateful ideology", adding that social media sites including Facebook and YouTube had also complied with the request.
The legal suit in France came a week after France's SPCJ Jewish security watchdog said anti-Semitic acts surged by 45 percent since the start of the year and were given new impetus by attacks by Islamic extremist Mohamed Merah.
Merah went on a shooting rampage in March in and around the city of Toulouse, killing a rabbi, three Jewish children and three French paratroopers before being shot dead in a police siege.
Twitter was forced to apologise in July for suspending the account of a British journalist in an incident which prompted accusations it favoured its commercial ties with Olympics broadcaster NBC over media freedoms.
The move came after an outcry over the suspension of Guy Adams, Los Angeles correspondent for The Independent, who had tweeted his outrage over NBC's delay in broadcasting the opening ceremony in order to catch the prime-time audience.
The case did not stem from an official request to block an account.
British police have also investigated messages published on the Twitter account of British National Party chief Nick Griffin who tweeted the address of a gay couple who won a landmark court ruling on discrimination, ending with message: "Say no to heterophobia!"
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