"It is not acceptable that they have previously sent witnesses who seek to avoid answering difficult questions by claiming not to know the answers," Collins said in a statement.

Over the weekend, Facebook was on the defensive. Top executives took to Twitter to argue that the company's protections had not been breached, and that Facebook was thus not at fault.

"This was unequivocally not a data breach," tweeted Andrew Bosworth, a Facebook executive. "No systems were infiltrated, no passwords or information were stolen or hacked."

The calls for greater scrutiny followed reports on Saturday that Cambridge Analytica, a political data firm founded by Steve Bannon and Robert Mercer, the wealthy Republican donor, had used the Facebook data to develop methods that it claimed could identify the personalities of individual US voters and influence their behaviour.

The firm's so-called psychographic modelling underpinned its work for the Trump campaign in 2016, though many have questioned the effectiveness of its techniques.