A US congressional committee said on Tuesday it was discussing a date with Facebook for chief executive Mark Zuckerberg to testify as part of an ongoing probe into how a political consultancy came to be in receipt of personal data on 50 million Facebook users.

Elena Hernandez, spokeswoman for the House Committee on Energy and Commerce, said: "The committee is continuing to work with Facebook to determine a day and time for Mr. Zuckerberg to testify."

Read more: What role did Cambridge Analytica play in the Brexit vote?

Facebook confirmed on Tuesday it had received invitations to testify before Congress and that it was talking to legislators.

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

The Federal Trade Commission said on Monday that it had also opened an investigation into the company, citing media reports raising what it called "substantial concerns about the privacy practices of Facebook."

Cambridge Analytica and data mining

Lawmakers in the US and Europe want to know more about the company's role in consultancy Cambridge Analytica's use of the data to target US and British voters in close-run elections in 2016 and 2015, respectively.

Whistleblower Christopher Wylie told UK lawmakers during a committee hearing on Tuesday that a firm linked to Cambridge Analytica had helped the official Brexit Vote Leave campaign avoid campaign financing laws during the referendum.

He said that the official campaign's "cheating" may well have swayed the EU referendum result.

Facebook shares dropped 4.9 percent on Tuesday and have fallen almost 17 percent since March 16, when Facebook acknowledged that user data had been improperly channeled to Cambridge Analytica, which was hired by Donald Trump's 2016 presidential campaign.

London ‘astonished'

Facebook said on Tuesday that it would send one of the CEO's deputies to London, suggesting Chief Technology Officer Mike Schroepfer or Chief Product Officer Chris Cox, who "had the expertise to answer questions on the complex subject" in April.

Damian Collins, the chair of a British committee of MPs investigating the effects of fake news on UK democracy, said on Tuesday that Zuckerberg's decision to send other executives to the UK to answer questions on his behalf was "absolutely astonishing" and urged him to think again.

Last October, Facebook sent general counsel, Colin Stretch, for two days of congressional hearings.

‘Fixing' Facebook

Zuckerberg said earlier this year his personal goal was to "fix" Facebook after a series of PR mishaps for the giant social media company.

Zuckerberg and chief operating officer, Sheryl Sandberg, have been warning that the company was being manipulated in ways its creators never intended.

The company acknowledged last September that it had sold advertisements to Russian agents seeking to influence the US presidential election.

jbh/bw (dpa, AFP, Reuters)

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