US intelligence leaker Edward Snowden said in an interview released Tuesday he chose to divulge details of a vast US surveillance effort to journalists who reported "fearlessly" on controversial subjects.

Snowden, in the interview released by The New York Times, said he chose documentary filmmaker Laura Poitras and Guardian reporter Glenn Greenwald because they were not cowed by the US government.

"After 9/11, many of the most important news outlets in America abdicated their role as a check to power -- the journalistic responsibility to challenge the excesses of government -- for fear of being seen as unpatriotic and punished in the market during a period of heightened nationalism," Snowden was quoted as saying in an encrypted conversation with journalist Peter Maass for the Times Sunday magazine.

"Laura and Glenn are among the few who reported fearlessly on controversial topics throughout this period, even in the face of withering personal criticism, and resulted in Laura specifically becoming targeted by the very programs involved in the recent disclosures."

He said Poitras "demonstrated the courage, personal experience and skill needed to handle what is probably the most dangerous assignment any journalist can be given -- reporting on the secret misdeeds of the most powerful government in the world -- making her an obvious choice."

Snowden, who was granted asylum in Russia after spending over five weeks in a Moscow airport transit zone, is said by his lawyers to now be at an undisclosed secret location.

The United States wants to put Snowden on trial for leaking details of vast American surveillance programs but Moscow has steadfastly refused to hand him over.

A former contractor, Snowden released details of secret National Security Agency programs aimed at thwarting terrorism which sweep up vast amounts of phone and Internet data.

Snowden said that when he met the two journalists in Hong Kong for a filmed interview, "I think they were annoyed that I was younger than they expected, and I was annoyed they had arrived too early, which complicated the initial verification."

He said Poitras "was more suspicious of me than I was of her, and I'm famously paranoid."

Snowden added that he was surprised that Greenwald did not agree to his requests to encrypt all communications.

"This is 2013, and a journalist who regularly reported on the concentration and excess of state power," he said.

"I was surprised to realize that there were people in news organizations who didn't recognize any unencrypted message sent over the Internet is being delivered to every intelligence service in the world. In the wake of this year's disclosures, it should be clear that unencrypted journalist-source communication is unforgivably reckless."