Oliver Stone, never one to run scared from a controversy, yesterday waded into the ongoing NSA debate, defending the American whistlebower Edward Snowden and hailing him as a "hero" for exposing the US's mass surveillance programme.

"It's a disgrace that Obama is more concerned with hunting down Snowden than reforming these George Bush-style eavesdropping techniques," the Oscar-winning director told audiences at the Karlovy Vary international film festival in the Czech Republic.

Snowden, 30, is living in a transit zone in a Moscow airport where he is seeking asylum from federal prosecution in the US. He is believed to have applied for asylum in 20 countries - thus far without result. In the meantime, his revelations have sparked a diplomatic crisis. In the past few days both the German and French leaders have described the NSA's surveillance program as "unacceptable".

"To me Snowden is a hero because he revealed secrets that we should all know, that the United States has repeatedly violated the fourth amendment," Stone said. "He should be welcomed and offered asylum. But he has no place to hide because every country is intimidated by the United States."

Stone, 66, was at the festival to unveil episodes of his new Showtime TV series, Oliver Stone's Untold History of the United States, as well as the extended "ultimate" cut of his unloved 2004 epic Alexander.

The film-maker's vocal support for Snowden is entirely in character. In recent months Stone has also thrown his weight behind WikiLeaks founder Julian Assange, visiting the activist at his base at the Ecuadorian embassy in London and criticising the depiction of Assange in two upcoming Hollywood pictures. "Julian Assange did much for free speech," Stone has said. "And he is now being victimised by the abusers of the concept."