Allegations about the mass harvesting of Facebook users' data are "very concerning", Downing Street has said.
Prime Minister Theresa May's official spokesman called on the social media giant and data firm Cambridge Analytica to co-operate fully with an investigation by Information Commissioner Elizabeth Denham.
CA was suspended from Facebook last week after it emerged that data on millions of users had not been destroyed as agreed.
Whistleblower Chris Wylie, a former research director at the UK-based company, told Channel 4 News a so-called data grab had been carried out on more than 50 million profiles in 2014.
Reports in The Observer suggested that the information was used to target political advertising in the 2016 US presidential election.
Damian Collins, chairman of the House of Commons Digital, Culture, Media and Sport Committee, has called on Facebook founder Mark Zuckerberg to appear before MPs to explain his company's actions.
Asked about the reports, Mrs May's spokesman said: "The allegations are clearly very concerning.
"It is essential that people can have confidence that their personal data will be protected and used in an appropriate way.
"It is absolutely right that the Information Commissioner is investigating this matter.
"We expect Facebook, Cambridge Analytica and all the organisations involved to co-operate fully."
In a response to its suspension from Facebook, Cambridge Analytica said it fully complied with Facebook's terms of service.