A 29-year-old government contractor has revealed himself as the source of disclosures about America's secret surveillance programmes.
Edward Snowden, a former CIA technician who has worked for the National Security Agency (NSA), said he had leaked information to The Guardian and The Washington Post because the public needs to decide whether the programmes are right or wrong.
"I do not want to live in a world where everything I do and say is recorded. That is not something I am willing to support or live under," he told The Guardian.
"My sole motive is to inform the public as to that which is done in their name and that which is done against them."
He said he was willing to sacrifice a comfortable life "because I can't in good conscience allow the US government to destroy privacy, internet freedom and basic liberties for people around the world with this massive surveillance machine they're secretly building".
The recent stories in The Guardian and The Washington Post have revealed the existence of a surveillance system, code-named Prism, that was set up by the NSA to track the use of the internet directly from ISP servers.
Mr Snowden used the name "Verax", truth-teller in Latin, when he first approached The Post with his bomb-shell revelations. Now, though to be holed up in Hong Kong, he risks prosecution.
The leaks have led the NSA to ask the Justice Department to conduct a criminal investigation. The Justice Department said it was in the initial stages of an inquiry.
Mr Snowden worked for the NSA as an employee of various outside contractors, including Dell and Booz Allen Hamilton, his current employer.
He flew to Hong Kong on May 20 after copying the last set of documents he intended to disclose at the NSA's office in Hawaii, the reports said. He is understood to have checked out of the Kowloon hotel there on Monday.
The Guardian and The Washington Post said they had revealed Mr Snowden's identity at his own request.
"I'm not going to hide," Mr Snowden told The Post. "Allowing the US government to intimidate its people with threats of retaliation for revealing wrongdoing is contrary to the public interest."
He acknowledged fears of being "rendered" - summarily detained by the CIA or its partners without due process - or taken in for questioning by Chinese authorities.
Mr Snowden said he is seeking "asylum from any countries that believe in free speech and oppose the victimisation of global privacy".
"The nation that most encompasses this is Iceland. They stood up for people over internet freedom."
Iceland's International Modern Media Institute, a free press group, said it had yet to hear from Mr Snowden directly.
But in a statement the institute said it would do what it could to help him find asylum and was working to set up a meeting with Iceland's interior minister.
However, Mr Snowden could be extradited to the United States under an extradition treaty between Washington and Hong Kong, a semi-autonomous territory of China and former British colony that has a long-standing tradition of cooperation with America on legal matters.
House intelligence committee member Peter King called for Mr Snowden's immediate extradition and prosecution, saying "the leaker has done extreme damage to the US".
WikiLeaks founder Julian Assange said Mr Snowden was a "hero" for alerting the world to the emergence of a "mass surveillance state".
Speaking from London's Ecuadorian embassy, where he has been taking refuge for almost a year, Mr Assange told Sky News: "It's very pleasing to see such clear and concrete proof presented to the public."
He warned that Mr Snowden is in a "very serious" position as the US weighs up what action to take against him.
He said: "I have absolutely no doubt that a very serious and aggressive action will be directed against Mr Snowden.
"What other countries need to do is line up to give support for him. Everyone should go to their politicians and press and demand that they offer Mr Snowden asylum in their country."
The Prism revelations sparked an outcry, which grew when The Guardian said the UK's GCHQ monitoring centre has been accessing information about British citizens through Prism.
Both Prime Minister David Cameron and Foreign Secretary William Hague have insisted that the UK's intelligence services operate within the law and are subject to proper scrutiny.
A separate programme, also disclosed by The Guardian, has been used to obtain the telephone records of millions of Americans.
President Barack Obama described the secret programmes as vital to keeping Americans safe, saying the US is "going to have to make some choices between balancing privacy and security to protect against terror".
Mr Snowden said he has no regrets, even though he fears he may not see his home again.
A native of North Carolina, Mr Snowden said he did not have a high school diploma and enlisted in the US Army in 2003 because he wanted to fight in Iraq.
He was discharged after breaking his legs in training and took a job as a security guard at an NSA facility in Maryland.
He later joined the CIA where he worked on IT security. He said he started becoming disillusioned during a stint in Geneva where he had access to classified documents.
"I realised that I was part of something that was doing far more harm than good," he was quoted as saying.
He left the CIA in 2009 and joined a private contractor that assigned him at an NSA facility in Japan, where, he said, he "watched as Obama advanced the very policies that I thought would be reined in".
His current employer, Booz Allen, said Mr Snowden had worked there "for less than three months". The firm promised to work with the authorities on the investigation.
The director of national intelligence, James Clapper, said two plots had been foiled using information obtained through Prism and phone snooping programmes.
Both were in 2009, he said. One was a bomb attack on the New York subway, and the other was linked to David Headley, a conspirator in the 2008 Mumbai attacks.
Under Prism, which has been running for six years, the NSA can tap Google, Yahoo, Facebook and other Silicon Valley giants to lift emails, online chats, pictures, files and videos uploaded by foreign users.
Companies including Google and Facebook have denied knowledge of the programme, insisting they have only provided user information to the authorities when compelled to by law.