The leaks have reopened the post-Sept. 11 debate about privacy concerns versus heightened measure to protect against terrorist attacks, and led the NSA to ask the Justice Department to conduct a criminal investigation into the leaks.
The Guardian, the first paper to disclose the documents, said it was publishing the identity of Edward Snowden, a former technical assistant for the CIA and current employee of defense contractor Booz Allen Hamilton, at his own request.
"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 newspaper.
Stories in The Guardian and The Washington Post published over the last week revealed two surveillance programs.
One of them is a phone records monitoring program in which the NSA gathers hundreds of millions of U.S. phone records each day, creating a database through which it can learn whether terror suspects have been in contact with people in the U.S. The Obama administration says the NSA program does not listen to actual conversations.
Separately, an Internet scouring program, code-named PRISM, allows the NSA and FBI to tap directly into nine U.S. Internet companies to gather all Internet usage - audio, video, photographs, emails and searches. The effort is designed to detect suspicious behavior that begins overseas.
Snowden said claims the programs are secure are not true.
"Any analyst at any time can target anyone. Any selector. Anywhere. Where those communications will be picked up depends on the range of those sensor networks and the authority that that analyst is empowered with," Snowden said, in accompanying video on the Guardian's website. "Not all analysts have the power to target anything. But 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."
He told the Post that he would "ask for asylum from any countries that believe in free speech and oppose the victimization of global privacy" in an interview from Hong Kong, where he is staying.
"I'm not going to hide," Snowden told the Post. "Allowing the U.S. government to intimidate its people with threats of retaliation for revealing wrongdoing is contrary to the public interest."
The Post declined to elaborate on its reporting about Snowden.
Spokespeople for the White House, the Director of National Intelligence, NSA and CIA did not have immediate comment on the disclosures, nor would they confirm whether Snowden worked at the U.S. intelligence agencies.
In a statement, Booz Allen confirmed that Snowden "has been an employee of our firm for less than 3 months, assigned to a team in Hawaii." The statement said if the news reports of what he has leaked prove accurate, "this action represents a grave violation of the code of conduct," and the company promised to work closely with authorities on the investigation.
Director of National Intelligence James Clapper has decried the revelation of the intelligence-gathering programs as reckless and said it has done "huge, grave damage." In recent days, he took the rare step of declassifying some details about them to respond to media reports about counterterrorism techniques employed by the government.
Snowden told The Guardian that he lacked a high school diploma and enlisted 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 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, which said he asked to be identified after several days of interviews.
Snowden could face decades in a U.S. jail for revealing classified information if he is successfully extradited from Hong Kong, said Mark Zaid, a national security lawyer who represents whistleblowers. Hong Kong has an extradition treaty with the United States that took force in 1998, according to the U.S. State Department website.
"If it's a straight leak of classified information, 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 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.
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 Wikileaks.
"They could say the revelation of the (NSA) programs could instruct people to change tactics," Zaid said. But even under the lesser charges of simply revealing classified information, "you are talking potentially decades in jail, loss of his employment and his security clearance."
Officials said the revelations were dangerous and irresponsible. House intelligence committee member Peter King, R-NY, called for Snowden to be "extradited from Hong Kong immediately...and prosecuted to the fullest extent of the law," in an interview with The Associated Press Sunday.
"I believe the leaker has done extreme damage to the U.S. and to our intelligence operations," King said, by alerting al-Qaida to U.S. surveillance, and by spooking U.S. service providers who now might fight sharing data in future with the U.S. government, now that the system has been made public.
King added that intelligence and law enforcement professionals he'd spoken to since the news broke were also concerned that Snowden might be taken into custody by Chinese intelligence agents and questioned about CIA and NSA spies and policies.
"To be a whistleblower, there would have to be a pattern of him filing complaints through appropriate channels to his supervisors," said Ambassador John Negroponte, the first director of national intelligence, in an interview with the AP Sunday. "For me, it's just an outright case of betrayal of confidences and a violation of his nondisclosure agreement."
President Barack Obama, Clapper and others have said the programs are authorized by Congress and subject to strict supervision of a secret court.
"It's important to recognize that you can't have 100 percent security and also then have 100 percent privacy and zero inconvenience," Obama said. "We're going to have to make some choices as a society."