whistleblower

Frances Haugen, a 37-year-old former product manager turned whistleblower, heavily criticised the company at a hearing on Capitol Hill.

Facebook however said Ms Haugen spoke about areas she has no knowledge of.

It comes amid growing scrutiny of the social media giant and increasing calls for its regulation.

Facebook is the world's most popular social media site. The company says it has 2.7 billion monthly active users. Hundreds of millions of people also use the company's other products, including WhatsApp and Instagram.

The director was speaking at the Toronto International Film Festival, where Snowden had its world premiere.

Joseph Gordon-Levitt plays the US National Security Agency contractor who fled to Russia in 2013 having revealed extensive internet and phone surveillance by US intelligence.

The cast includes Melissa Leo, Zachary Quinto and Shailene Woodley.

"This is a secret underworld and no one in the NSA has come forward," Stone told a press conference on Saturday.