"Fifty million people lost their privacy," Feinstein told reporters at the U.S. Senate, amid mounting calls in Congress for the social media company to account for the mining of its users' personal data by a political consultancy hired by President Donald Trump's campaign.

"I think that we ought to have the head of Facebook, not their lawyer, not their number two, but their number one, come... state if they're really prepared to lead the industry to some controls that prevent all this from happening," she said.

(Reporting by Patricia Zengerle; Editing by Nick Zieminski)