On the same day, Zuckerberg turned down British lawmakers' invitations to explain to a British parliamentary committee what went wrong.

The company said it would instead send one of his deputies, suggesting that Chief Technology Officer Mike Schroepfer or Chief Product Officer Chris Cox had the expertise to answer questions on the complex subject.

The head of the committee called Zuckerberg's decision "astonishing" and urged him to think again.

Facebook shares were down 3.3 per cent on Tuesday and have fallen almost 17 per cent since March 16, when Facebook first acknowledged that user data had been improperly channeled to Cambridge Analytica, which was hired by Donald Trump's 2016 presidential campaign.

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The revelations have raised investor concerns that any failure by big tech companies to protect privacy could deter advertisers and lead to tougher regulation.

It was unclear when or before which committee Zuckerberg would testify.

The US Senate Judiciary Committee said on Monday it had invited Zuckerberg, as well as the CEOs of Alphabet Inc and Twitter to testify at an April 10 hearing on data privacy.

The US House Energy and Commerce Committee and US Senate Commerce Committee had already formally asked Zuckerberg to appear at a congressional hearing.

The US Federal Trade Commission took the unusual step of announcing on Monday that it had opened an investigation into the company - which it generally only does in cases of great public interest - citing media reports that raise what it called "substantial concerns about the privacy practices of Facebook."