The UN rights chief decried Wednesday an online "trolling campaign" against a leading anti-defamation group, urging online platforms like X, formerly Twitter, to do more to battle hate speech.

United Nations High Commissioner for Human Rights Volker Turk demanded that social media platforms "do far more to stop the circulation of hate speech and disinformation".

"Those that do not take action need to be held to account," he said, insisting "there is no excuse for purveying the voice of hatred".

Speaking at an event on anti-Semitism on the sidelines of the UN Human Rights Council in Geneva, Turk deplored in particular "the current trolling campaign of one online platform against the anti-Defamation League, after it called for action to limit its volume of hate speech".

Turk did not mention names, but appeared to be referring to a barrage of abuse recently launched by X owner Elon Musk's against the US-based Jewish organisation.

Musk has accused the ADL of making unfounded accusations of anti-Semitism that have scared away advertisers and hurt his company's revenue, and has threatened to sue for billions of dollars.

Musk, who bought Twitter last year and rebranded it as X, has come under fire for liking posts on the platform with the hashtag "BanTheADL".

The hateful campaign started after the ADL participated in a civil rights march marking the 60th anniversary of Martin Luther King's "I have a dream" speech, according to the group.

The ADL has for years accused the social media site of amplifying anti-Semitic hate speech, and has charged that problematic and racist speech has risen sharply on X after Musk completed his $44 billion takeover in October.

The organisation recently met with X top executives to discuss the problem.

Turk decried Wednesday that "new technologies and online media mean that racist caricatures and conspiracy theories can circulate now at a much greater speed and without regard to distance, making them a grave threat to our social fabric.

"Social media platforms have played a terrible role in metastasising of hatred from limited backwaters into multi-current mainstream trends," he said.

Turk insisted that social media companies needed to "increase transparency about their hate speech policy".

"And they must much more effectively put these policies into practice, including by ensuring that people can report hate speech easily and that those reports will swiftly lead to appropriate action," he said.

The UN rights chief also urged all digital platforms "to vastly improve their efforts to combat hate speech in languages other than English, and pivot even greater attention to areas where early warning ... shows that there is a rise in hate".