Politicians in Britain and the US are pushing for Facebook's Chief Executive Mark Zuckerberg to appear before them to answer questions about the scandal involving the data breach of millions of its users.

Facebook is set to brief the US Congress on Wednesday.

Cambridge Analytica, a political consultancy based in London, is accused of gaining unauthorised access to the details of 50 million Facebook users. The firm worked for Donald Trump's presidential campaign and the Brexit campaign in the UK.

Its chief executive has been suspended. He was secretly recorded boasting about the firm's ability to sway elections.

News of the scandal hit Facebook shares. The company's stock fell 2.5 percent on Tuesday, that followed an almost seven percent drop on Monday.

Over $60bn has been wiped off the company's value over the last two days.

Al Jazeera's Sonia Gallego reports from London.