Washington DC - President Joe Biden blasted Meta Friday for scrapping fact-checking on Facebook and Instagram in the US, calling the move "really shameful" after a global network warned of real-world harm if the tech giant expands its decision to other countries.

Meta chief executive Mark Zuckerberg triggered alarm Tuesday when he announced the Palo Alto company was ditching third-party fact-checking in the US and turning over the task of debunking falsehoods to ordinary users under a model known as "Community Notes," popularized by X.

The decision was widely seen as an attempt to appease President-elect Donald Trump, whose conservative support base has long complained that fact-checking on tech platforms was a way to curtail free speech and censor right-wing content.

"I think it's really shameful," Biden told reporters at the White House when asked about the announcement.

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"Telling the truth matters," he said, adding that the move was "completely contrary to everything America's about."

The International Fact-Checking Network has warned of devastating consequences if Meta broadens its policy shift beyond US borders to the company's programs covering more than 100 countries.

"Some of these countries are highly vulnerable to misinformation that spurs political instability, election interference, mob violence and even genocide," IFCN, which has dozens of global member organizations, said in an open letter to Zuckerberg.

"If Meta decides to stop the program worldwide, it is almost certain to result in real-world harm in many places," it added.

Zuckerberg doubled down in an interview Friday with podcaster Joe Rogan, comparing the fact-checking program with "something out of 1984," in a reference to George Orwell's dystopian novel. He added that the program, which began in 2016, was "destroying so much trust, especially in the United States."

Zuckerberg also expressed regret for giving "too much deference" to the traditional media, criticizing it for pushing the narrative that social media misinformation had swung the 2016 election in favor of Trump.

Zuckerberg stunned many when he said on Tuesday that fact-checkers were "too politically biased," and added that the program had led to "too much censorship."

IFCN's letter rejected the claim as "false," insisting that Meta's fact-checking partners underwent "rigorous" verification to meet its strict nonpartisanship standards.

Far from questioning those standards, it added, Meta had "consistently praised their rigor and effectiveness."

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The United Nations rights chief Volker Turk also insisted on Friday that regulating harmful content and hate speech online "is not censorship."

Allowing such content to flourish online has "real-world consequences," Turk said on X.

Brazil on Friday gave Meta 72 hours to explain its fact-checking policy for the country, and how it plans to protect "fundamental rights" on its platforms. Attorney General Jorge Messias told journalists his office could take "legal and judicial" measures against Meta if it does not respond in time to an extrajudicial notice filed Friday.

Facebook currently pays to use fact checks from around 80 organizations globally on the platform, as well as on WhatsApp and Instagram.

"Understandably this policy from Meta is aimed at US users, but we cannot be certain how it will affect other countries," Supinya Klangnarong, co-founder of Thai fact-checking platform Cofact, told AFP.

"By allowing the proliferation of hate speech and racist dialogue could be a trigger towards violence."

Cofact is not an accredited member of the IFCN or of Facebook's fact-checking scheme.

Fears over a possible spike in hate speech have grown as Meta also rolled back restrictions around topics such as gender and sexual identity.

The latest version of Meta's community guidelines said its platforms would now permit users to accuse people of "mental illness or abnormality" based on their gender or sexual orientation.

Meta's policy overhaul came less than two weeks before Trump takes office.

Trump has been a harsh critic of Meta and Zuckerberg for years, accusing the company of bias against him and threatening to retaliate against the tech billionaire once back in office.

Zuckerberg recently donated a large sum of money to Trump's inauguration fund in an apparent attempt to bury the hatchet.