Facebook Chief Executive Mark Zuckerberg will meet with leaders of the European Parliament today to answer questions about how the data of millions of Facebook users ended up in the hands of a political consultancy.

The meeting comes three days before tough new European Union rules on data protection take effect. Companies will be subject to fines of up to 4 percent of global turnover for breaching them.

Facebook has come under scrutiny from politicians on both sides of the Atlantic after it emerged that Cambridge Analytica, a British political consultancy that worked on US President Donald Trump's campaign, improperly acquired the data of 87 million users, including up to 2.7 million in the EU.

Zuckerberg has apologised for the leak in testimony to the US Congress, but questions remain over how the company's data policies let the leak happen.

Zuckerberg will stress Facebook's commitment to Europe, where it will employ 10,000 people by the end of the year, according to pre-released remarks.

"I believe deeply in what we're doing. And when we address these challenges, I know we'll look back and view helping people connect and giving more people a voice as a positive force here in Europe and around the world," Zuckerberg is expected to say.

He will also apologise for failing "to take a broad enough view" of the company's responsibilities, "whether it’s fake news, foreign interference in elections or developers misusing people’s information."

Zuckerberg will meet with the president of the European Parliament, Antonio Tajani, the leaders of the parliament's political groups and the chair of the civil liberties committee, Claude Moraes.

The meeting will be livestreamed after an outcry over plans to hold it in private.

Since the Cambridge Analytica scandal, Facebook has suspended 200 apps from its platforms as it investigates third-party apps that have access to large quantities of user data.

Cambridge Analytica and its British parent, SCL Elections Ltd, have declared bankruptcy and closed down.