WASHINGTON - US fugitive intelligence leaker Edward Snowden "trained as a spy" and worked "undercover overseas" for intelligence agencies, he told NBC News in excerpts of an interview aired Tuesday.

In his first interview in US media, Snowden hit back at claims that he was merely a low-level contractor, saying he worked "at all levels from -- from the bottom on the ground, all the way to the top."

Snowden, who has been charged in the United States with espionage, was granted asylum by Russia in August 2013 after shaking the American intelligence establishment to its core with a series of leaks on mass surveillance in the United States and around the world.

In the interview, taped last week and to air in full on Wednesday, Snowden defended himself against claims minimizing his intelligence experience before he stole and leaked a trove of classified documents revealing the NSA's program of phone and Internet surveillance.

"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," he said.

He said he had worked covertly as "a technical expert" for the Central Intelligence Agency and the National Security Agency, as well as as a trainer for the Defense Intelligence Agency.

"I don't work with people. I don't 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 said.

"So when they say I'm a low-level systems administrator, that I don't know what I'm talking about, I'd say it's somewhat misleading."

Snowden, who left high school at 15 without graduating, made his revelations three months into his new job with the consulting firm Booz Allen Hamilton as a systems administrator based at the NSA's threat operations center in Hawaii.

Following the leaks, he proceeded to Hong Kong unaccompanied, where he checked into a hotel without a plan.

On June 23 he headed to Moscow, two days after his 30th birthday, where he holed up in the Sheremetyevo Airport for days before he was eventually granted asylum.

Snowden was "profoundly at peace" with his decision to leak national security documents, and even joked about the consequences, journalist Glenn Greenwald, who broke the Snowden story for Britain's Guardian newspaper, said in a new book released two weeks ago.

Meanwhile the US House of Representatives passed landmark reforms Thursday curbing bulk collection of Americans' telephone records, the first step toward restricting intelligence-gathering by the NSA since Snowden divulged the secret program.