London (AFP) - British MPs renewed a demand on Tuesday to interview Facebook chief Mark Zuckerberg over a data privacy row that has rocked the social media giant, after he responded to an earlier request by offering to send one of his deputies.

Damian Collins, the chairman of the House of Commons digital, culture and media committee, said the seriousness of the allegations meant it was "appropriate" for Zuckerberg to offer an explanation himself, whether in person or via video-link.

His comments came amid renewed pressure from the European Union to disclose more details about how up to 50 million users' data are alleged to have been taken from Facebook and used in political campaigns.

In a letter published by the British committee on Tuesday, Facebook offered to send chief technology office Mike Schroepfer or chief product officer Chris Cox to London next month to provide answers.

"We'd be very happy to invite Mr Cox to give evidence. However we would still like to hear from Mr Zuckerberg as well," Collins said at the start of a committee hearing on Tuesday.

"We will seek to clarify with Facebook whether he is available to give evidence or not, because that wasn't clear from our correspondence.

"And if he is available to give evidence, then we would be happy to do that either in person or via video link if that would be more convenient for him."

The EU has given the social media giant two weeks to answer its own queries over the scandal, which has heavily hit Facebook's share price and raised major questions over how social media companies use private data.

EU justice commissioner Vera Jourova wrote to Facebook chief operating officer Sheryl Sandberg, asking what measures the company plans to take to prevent a similar scandal.

She also asked whether stricter rules were needed for companies like Facebook as exist for traditional media, and whether it would change its approach on transparency toward users and regulators.

- Address questions 'at senior level' -

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Facebook insists it did not know the data taken from its site were being used by a British company, Cambridge Analytica, which worked on US President Donald Trump's election campaign among others.

However, its rules at the time allowed an app developed by an academic researcher, which was downloaded by an estimated 270,000 people, to take information from millions of their friends.

In her letter, Rebecca Stimson, head of public policy for Facebook UK, revealed that the tech giant was working with regulators around the world to assess how many people in each country were affected.

"We can now confirm that around one percent of the global downloads of the app came from users in the EU, including the UK," she wrote.

Amid investigations by lawmakers in Europe and the United States, Zuckerberg has taken out adverts in US, British and German newspapers in recent days apologising for the "breach of trust".

But the company is struggling to contain the growing crisis.

US consumer protection agency, the Federal Trade Commission, on Monday confirmed it had opened an investigation into whether Facebook mishandled private data or violated a 2011 agreement which settled an earlier probe.

In her letter to the British committee, Stimson said: "Facebook fully recognizes the level of public and parliamentary interest in these issues and support your belief that these issues must be addressed at the most senior levels of the company by those in an authoritative position to answer your questions.

"As such, Mr Zuckerberg has personally asked one of his deputies to make themselves available to give evidence in person to the committee."

She said either Schroepfer or Cox could attend "straight after the Easter parliamentary recess", meaning April 16 at the earliest.