In an interview with Wired magazine in Moscow, where he sought asylum after the revelations, Snowden said he had long been troubled by the activities of the National Security Agency (NSA), which employed him as a contractor.

But it was only when Director of National Intelligence James Clapper told lawmakers that the agency does "not wittingly" collect data on millions of American citizens that he was angry enough to act.

The magazine released the article online Wednesday, along with several new photographs of the once-elusive Snowden, including a cover shot of the technician lovingly cradling an American flag.

Snowden says he made his decision to leave his office in Hawaii and head to Hong Kong with secret documents on thumb drives after reading in March 2013 about Clapper briefing a Senate committee.