Edward Snowden, former contractor at the US National Security Agency who leaked top secret documents about massive surveillance programmes conducted by the US government, said he "was trained as a spy" and rejected claims that he was a low-level analyst.

An excerpt from his interview in Moscow with NBC showed Snowden claiming that he was a spy assisting US agencies CIA and NSA in undercover operations overseas. The interview will be aired at 10:00 pm ET on 28 May.

"It's no secret that the US tends to get more and better intelligence out of computers nowadays than they do out of people," Snowden told NBC news anchor Brian Williams.

"I was trained as a spy in sort of the traditional sense of the word in that I lived and worked undercover overseas - pretending to work in a job that I'm not - and even being assigned a name that was not mine."

Snowden described himself as a "technical expert" in the interview, adding that he did not "recruit agents".

"What I do is I put systems to work for the United States. And I've done that at all levels from - from the bottom on the ground all the way to the top," he added.

"Now, the government might deny these things, they might frame it in certain ways and say, 'Oh well, you know, he's - he's a low-level analyst."

Snowden received international attention after he leaked up to 1.7 million top secret documents about the NSA's surveillance programmes.

The Obama administration faced severe criticism across the globe as the documents revealed that the NSA tapped telephone conversations and spied on the internet activities of prominent people, including German chancellor Angela Merkel and Brazilian president Dilma Rousseff.

Snowden fled the US in May 2013 and has been living under temporary asylum in Russia. He is wanted by the US on charges of espionage and theft of government property.

Germany's Der Spiegel, citing Snowden's German lawyer Wolfgang Kaleck, earlier reported that the whistleblower is "considering' returning to the US under certain conditions.