WATCH LIVE: Mark Zuckerberg faces grilling in European Parliament over Facebook data scandal

Facebook chief Mark Zuckerberg faces tough questions later Tuesday at the European Parliament over the fallout from the Cambridge Analytica data breach scandal.

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The social network boss's appearance will be livestreamed to the public after angry EU lawmakers objected to initial plans to host the hearing in Brussels behind closed doors.

His grilling by the heads of the parliament's political groups at around 1630 GMT comes three days before the EU introduces sweeping new personal data protection rules, which the Facebook chief has now welcomed.

"Great news for EU citizens," European Parliament President Antonio Tajani tweeted on Monday about the decision to stream the hearing after days of bitter wrangling.

MEPs had demanded that Zuckerberg show the transparency the scandal calls for.

Facebook admitted that up to 87 million users may have had their data hijacked by British consultancy Cambridge Analytica, which worked for US President Donald Trump during his 2016 campaign.

The Silicon Valley social network has told the European Commission, the EU's executive arm, that the personal data of up to 2.7 million Europeans may have been sent inappropriately to Cambridge Analytica, which has since filed for bankruptcy in the US.

Tajani, who first invited the young American billionaire to testify before parliament back in March, will meet him around 1600 GMT, followed by parliamentary leaders.

The Italian politician has warned Zuckerberg it would be a "big mistake" for him not to answer questions from an elected body that regulates a market of 500 million people, many of them Facebook users.

Tajani said MEPs want to know if "people used data for changing the position of the citizens," including during the shock 2016 referendum for Britain to leave the EU.

In April, Tajani rejected Zuckerberg's initial offer to send a more junior executive in his place.

Objecting to the latest plans for a closed-door hearing, MEPs insisted Zuckerberg face a grilling similar to his 10-hour interrogation in US Congress last month.

- 'Hear the truth' -

Guy Vehofstadt, leader of the ALDE liberals group in parliament, had vowed to boycott the interrogation if it were not public.

"I will attend the hearing with Mr Zuckerberg as webstreaming makes it now transparent and public," Verhofstadt tweeted on Monday.

"EU citizens have been most affected by the recent scandal and deserve to hear the truth," the former Belgian premier said, inviting Europeans to send him questions for Zuckerberg.

Udo Bullmann, of the Progressive Alliance of Socialists and Democrats in the European Parliament, said it would have been a "farce" not to have a public event.

The Greens party said "pressure worked" on Zuckerberg.

EU Justice Commissioner Vera Jourova paid Zuckerberg a backhanded compliment in recent weeks for having admitted that the Facebook scandal showed the need for strict new rules despite the reluctance of the US internet giants.

The EU's General Data Protection Regulation (GDPR), which comes into effect on Friday, aims to give users more control over how their personal information is stored and used online, with big fines for firms that break the rules.

The laws will cover large tech companies like Facebook, Google, and Twitter that use personal data as an advertising goldmine, as well as firms like banks and also public bodies.

Zuckerberg, who has repeatedly apologised for the massive data breach, told the US Congress in April that the more stringent EU rules could serve as a model globally.