Joseph Gordon-Levitt

Toronto 2016: Snowden explores 'secret underworld' says Oliver Stone

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.