(CNN) -- Traitor or patriot? Low-level systems analyst or highly trained spy?
Slammed by top U.S. government officials and facing espionage charges in the United States, former National Security Agency contractor Edward Snowden defended his decision to leak documents about classified surveillance programs during an interview with NBC "Nightly News" broadcast Wednesday.
"I think it's important to remember that people don't set their lives on fire," Snowden said. "They don't walk away from their extraordinarily, extraordinarily comfortable lives ... for no reason."
Speaking to anchor Brian Williams in a Moscow hotel, Snowden said he considers himself a patriot, and he wouldn't have gone to such lengths to reveal secret U.S. government surveillance programs if he didn't have to.
"The reality is, the situation determined that this needed to be told to the public. The Constitution of the United States had been violated on a massive scale," Snowden told Williams. "Now, had that not happened, had the government not gone too far and overreached, we wouldn't be in a situation where whistleblowers were necessary."
The U.S. government, Snowden said, is using the threat of terrorism "to justify programs that have never been shown to keep us safe but cost us liberties and freedoms that we don't need to give up and our Constitution says we shouldn't give up."
NSA analysts, he said, "can actually watch people's Internet communications, watch their Internet correspondence, watch their thoughts as they type," he said, describing such government surveillance as an "extraordinary intrusion ... into the way you think."
He didn't specify when such a program would be used by the agency, but said seeing that program when he worked for the NSA astonished him.
Snowden has been living for nearly a year in Russia, where the government has granted him temporary asylum.
But he stressed he has no ties with the Russian government.
"I have no relationship with the Russian government at all," he told NBC. "I've never met the Russian President. I'm not supported by the Russian government. I'm not taking money from the Russian government. I'm not a spy."
In fact, Snowden said, he never planned to stay in Russia.
"I personally am surprised that I ended up here," he said. "The reality is I never intended to end up in Russia. I had a flight booked to Cuba onwards to Latin America, and I was stopped because the United States government decided to revoke my passport and trap me in the Moscow airport."
He hasn't been able to leave Russia since then. Snowden said he would eventually like to return to the United States.
"If I could go anywhere in the world, that place would be home," he told NBC.
Asked by Williams whether he considers himself a patriot, Snowden didn't hesitate.
"Yes, I do," he said.
That comment drew a sharp response from U.S. Secretary of State John Kerry, who spoke with the network earlier Wednesday.
"Patriots don't go to Russia. They don't seek asylum in Cuba. They don't seek asylum in Venezuela. They fight their cause here," Kerry told NBC. "Edward Snowden is a coward. He is a traitor. And he has betrayed his country. And if he wants to come home tomorrow to face the music, he can do so."
In another excerpt from the interview, Snowden sought to bolster his credentials, arguing that the U.S. government has tried to downplay his skills and work experience.
"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.
"Now, the government might deny these things. They might frame it in certain ways, and say, oh, well, you know, he's a low-level analyst.
"But what they're trying to do is they're trying to use one position that I've had in a career, here or there, to distract from the totality of my experience, which is that I've worked for the Central Intelligence Agency, undercover, overseas.
"I've worked for the National Security Agency, undercover, overseas. And I've worked for the Defense Intelligence Agency as a lecturer at the Joint Counterintelligence Training Academy, where I developed sources and methods for keeping our information and people secure in the most hostile and dangerous environments around the world."
Snowden continued: "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."
A spokeswoman for the NSA declined to comment Tuesday on the NBC report.
What Snowden leaked sparked a national debate about privacy and security.
President Barack Obama and military officials remain in support of mass, warrantless surveillance. But civil libertarians, technology companies and others oppose it, noting the lack of transparency.
CNN's Jose Pagliery and Jamie Crawford contributed to this report.