The revelations have reopened the post-Sept. 11 debate about individual privacy concerns versus heightened measures to protect the U.S. against terrorist attacks. The NSA has asked the Justice Department to conduct a criminal investigation into the leaks.
President Barack Obama said the programs are authorized by Congress and subject to strict supervision of a secret court, and Director of National Intelligence James Clapper says they do not target U.S. citizens.
But Snowden claims the programs are open to abuse.
"Any analyst at any time can target anyone. Any selector. Anywhere," Snowden said in a video on the Guardian's website. "I, sitting at my desk, had the authority to wiretap anyone, from you or your accountant to a federal judge to even the president if I had a personal email."
Some lawmakers have expressed similar concerns about the wide reach of the surveillance.
"I expect the government to protect my privacy. It feels like that isn't what's been happening," said Sen. Mark Udall, D-Colo., a member of the Senate Intelligence Committee. "Again, there's a line, but to me, the scale of it and the fact the law was being secretly interpreted has long concerned me," he said Sunday on CNN, adding that at the same time, he abhors leaks.
But the Senate intelligence committee chairman, Democrat Dianne Feinstein of California, contends the surveillance does not infringe on U.S. citizens' privacy, and that it helped disrupt a 2009 plot to bomb New York City's subways and played a role in the case against an American who scouted targets in Mumbai, India, before a deadly terrorist attack there in 2008. Feinstein spoke on ABC's "This Week."
Clapper has decried the revelation of the intelligence-gathering programs as reckless and said it has done "huge, grave damage."
The spokesman for the Director of National Intelligence Shawn Turner said intelligence officials are "currently reviewing the damage that has been done by these recent disclosures," and referred further comment to the Justice Department.
"Any person who has a security clearance knows that he or she has an obligation to protect classified information and abide by the law," he added.
The disclosures come as the White House deals with managing fallout from revelations that it secretly seized telephone records of journalists at The Associated Press and Fox News.
Snowden says he was a former technical assistant for the CIA and a current employee of defense contractor Booz Allen Hamilton, which released a statement Sunday confirming he had been a contractor with them in Hawaii for less than three months, and promising to work with investigators.
Snowden could face many years in prison for releasing classified information if he is successfully extradited from Hong Kong, according to Mark Zaid, a national security lawyer who represents whistleblowers.
Hong Kong, though part of China, is partly autonomous and has a Western-style legal system that is a legacy from the territory's past as a British colony. A U.S.-Hong Kong extradition treaty has worked smoothly in the past. Hong Kong extradited three al-Qaeda suspects to the U.S. in 2003, for example.
But the treaty comes with important exceptions. Key provisions allow a request to be rejected if it is deemed to be politically motivated or that the suspect would not receive a fair trial. Beijing may also block an extradition of Chinese nationals from Hong Kong for national security reasons.
"The government could subject him to a 10 or 20 year penalty for each count," with each document leaked considered a separate charge, Zaid said.
Snowden told the Guardian newspaper he believes the government could try to charge him with treason under the Espionage Act, but Zaid said that would require the government to prove he had intent to betray the United States, whereas he publicly made it clear he did this to spur debate.
"My sole motive is to inform the public as to that which is done in their name and that which is done against them," Snowden told the Guardian.
The government could also make an argument that the NSA leaks have aided the enemy - as military prosecutors have claimed against Army Pvt. Bradley Manning, who faces life in prison under military law if convicted for releasing a trove of classified documents through the Wikileaks website.
"They could say the revelation of the (NSA) programs could instruct people to change tactics," Zaid said. That could add more potential jail time to the punishment.
Snowden told the Post he was not going to hide.
"Allowing the U.S. government to intimidate its people with threats of retaliation for revealing wrongdoing is contrary to the public interest," he said in the interview published Sunday. Snowden said he would "ask for asylum from any countries that believe in free speech and oppose the victimization of global privacy."
Snowden told The Guardian he lacked a high school diploma and served in the U.S. Army until he was discharged because of an injury, and later worked as a security guard with the NSA.
He later went to work for the CIA as an information technology employee and by 2007 was stationed in Geneva, Switzerland, where he had access to classified documents.
During that time, he considered going public about the nation's secretive programs but told the newspaper he decided against it, because he did not want to put anyone in danger and he hoped Obama's election would curtail some of the clandestine programs.
He said he was disappointed that Obama did not rein in the surveillance programs.
"Much of what I saw in Geneva really disillusioned me about how my government functions and what its impact is in the world," he told The Guardian. "I realized that I was part of something that was doing far more harm than good."
Snowden left the CIA in 2009 to join a private contractor, and spent the last four years at the NSA, as a contractor with consulting giant Booz Allen Hamilton and, before that, Dell.
The Guardian reported that Snowden was working in an NSA office in Hawaii when he copied the last of the documents he planned to disclose and told supervisors that he needed to be away for a few weeks to receive treatment for epilepsy.
He left for Hong Kong on May 20 and has remained there since, according to the newspaper. Snowden is quoted as saying he chose that city because "they have a spirited commitment to free speech and the right of political dissent", and because he believed it was among the spots on the globe that could and would resist the dictates of the U.S. government.
"I feel satisfied that this was all worth it. I have no regrets," Snowden told The Guardian.