Edward Snowden, in an exclusive interview with "Nightly News" anchor Brian Williams, is fighting back against critics who dismissed him as a low-level hacker — saying he was “trained as a spy” and offered technical expertise to high levels of government.

Snowden defended his expertise in portions of the interview that aired at 6:30 p.m. ET on Nightly News. The extended, wide-ranging interview with Williams, his first with a U.S. television network, airs Wednesday at 10 p.m. ET on NBC.

WATCH: Brian Williams hosts live special with Snowden analysis at 11 p.m. ET

“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 said in the interview.

Play Facebook

Twitter

Embed autoplay autoplay Copy this code to your website or blog

Snowden described himself as a technical expert who has worked for the United States at high levels, including as a lecturer in a counterintelligence academy for the Defense Intelligence Agency and undercover work for the CIA and National Security Agency.

“But I am a technical specialist. I am a technical expert,” he said. “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.”

Last year, when Snowden began leaking details of NSA spying programs and left the country, administration officials played down his work history, using descriptions such as “systems administrator” to describe his role at the agency. In June, President Barack Obama himself told reporters: “No, I’m not going to be scrambling jets to get a 29-year-old hacker.”

Snowden told Williams that those terms were “misleading.”

In the Defense Intelligence Agency job, Snowden said, he “developed sources and methods for keeping our information and people secure in the most hostile and dangerous environments around the world.”

“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,” he said.

Play Facebook

Twitter

Embed autoplay autoplay Copy this code to your website or blog

The Defense Intelligence Agency confirmed to NBC News that Snowden, as a contractor, had spoken at three of their conferences. Two intelligence sources tell NBC that Snowden worked for the CIA at an overseas station in IT and communications.

The CIA declined to comment on Snowden’s employment or his role at the agency, instead referring to the testimony of Director of National Intelligence James Clapper, specifically his statement before the Senate Select Committee on Intelligence in January of this year:

“Snowden claims that he’s won and that his mission is accomplished. If that is so, I call on him and his accomplices to facilitate the return of the remaining stolen documents that have not yet been exposed, to prevent even more damage to U.S. security.”

The NBC News interview was conducted last week in Moscow after months of preparation. Russia has granted Snowden temporary asylum.

Williams has described the interview as “months in the making and cloaked in the secrecy of his life as a fugitive living in exile overseas.”

Snowden, now 30, left the government and later worked for private intelligence contractors inside NSA outposts, including in Japan and Hawaii.

Edward Snowden: A Timeline

Weigh in on whether you view Snowden as a #Patriot or a #Traitor.

While working for the contractors, he downloaded up to 1.7 million secret documents about U.S. intelligence-gathering and partnerships with foreign allies, according to U.S. officials, including some that revealed the extent of data collection from U.S. telephone records and Internet activity.

The United States charged him with espionage and revoked his passport. Snowden flew to Moscow but was unable to continue to Latin America because he no longer had a passport.

Among the revelations in the documents taken by Snowden was the NSA’s bulk collection of phone and Internet metadata from U.S. users, spying on personal communications of foreign leaders, and the NSA’s ability to tap undersea fiber-optic cables and siphon data.

Snowden documents also were the basis for three exclusive NBC News digital reports, on Jan. 27, Feb. 4 and Feb. 7, as well as a report on Nightly News, documenting operations by British cyber spies to monitor YouTube and other social media services and to use an array of “dirty tricks” against nations, hackers, terror groups, suspected criminals and arms dealers.

Obama appointed a review board that criticized the domestic data collection. In March the president recommended ending bulk domestic metadata collection, and last week the House passed a bill to end it.

NBC News' Robert Windrem contributed to this report.

Follow NBC News Investigations on Twitter and Facebook.