An ex-CIA employee working as a contractor at the U.S. National Security Agency revealed on Sunday it was he who leaked details of a top secret U.S. surveillance program, acting out of conscience to protect "basic liberties for people around the world."

Holed up in a hotel room in Hong Kong, Edward Snowden, 29, said he had thought long and hard before publicizing details of an NSA program code-named PRISM, saying he had done so because he felt the United States was building an unaccountable and secret espionage machine that spied on every American.

Snowden, a former technical assistant at the CIA, said he had been working at the super-secret NSA as an employee of contractor Booz Allen. He said he decided to leak information after becoming disenchanted with U.S. President Barack Obama, whom he said had continued the policies of predecessor George W. Bush.

"I don't want to live in a society that does these sort of things ... 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, which published a video interview with him on its website.

Both the Guardian and the Washington Post published revelations last week that U.S. security services had monitored data about phone calls from Verizon and Internet data from large companies such as Google and Facebook.

The news came just before - and grabbed much attention from - a U.S.-China summit at the weekend at which Obama confronted Chinese President Xi Jinping over allegations of cyber theft, which the Washington Post reported included data from nearly 40 U.S. military weapons programs.

In naming Snowden on Sunday, the newspapers said he had sought to be identified.

"The NSA has built an infrastructure that allows it to intercept almost everything," Snowden said in explaining his actions.

"With this capability, the vast majority of human communications are automatically ingested without targeting. If I wanted to see your emails or your wife's phone, all I have to do is use intercepts. I can get your emails, passwords, phone records, credit cards," he said.

Worked at NSA for four years

The Guardian said Snowden had been working at the NSA for four years as a contractor for outside companies.

Three weeks ago, he copied the secret documents at the NSA office in Hawaii and told his supervisor he needed "a couple of weeks" off for treatment for epilepsy, the paper said. On May 20 he flew to Hong Kong.

The CIA and the White House declined to comment, while a spokesman for the Director of National Intelligence would not comment directly about Snowden himself but said the intelligence community was reviewing damage done by the recent leaks.

"Any person who has a security clearance knows that he or she has an obligation to protect classified information and abide by the law," said the spokesman, Shawn Turner.

The NSA has requested a criminal probe into the leaked information. On Sunday, the U.S. Justice Department said it was in the initial stages of a criminal investigation following the leaks.

Booz Allen, a U.S. management and technology consultancy, said reports of the leaked information were "shocking and if accurate, this action represents a grave violation" of company policy.

It said Snowden had been employed by the company for less than three months and that it would cooperate with any investigations.

A spokesman for Dell Inc declined to comment on reports that Snowden had been employed at that company. In 2009, Dell acquired Perot Systems, a U.S. government contractor that did work for U.S. intelligence agencies.

Snowden's decision to reveal his identity and whereabouts lifts the lid on one of the biggest security leaks in U.S. history and escalates a story that has placed a bright light on Obama's extensive use of secret surveillance.

The exposure of the secret programs has triggered widespread debate within the United States and abroad about the vast reach of the NSA, which has expanded its surveillance dramatically since the September 11 attacks on Washington and New York in 2001.

U.S. officials say the agency operates within the law. Some members of Congress have indicated support for the NSA activities, while others pushed for tougher oversight and possible changes to the law authorizing the surveillance.

'One of the most significant leakers'

Snowden's decision to go public could expose him to the wrath of the U.S. authorities. The Guardian compared him to Bradley Manning, an American soldier now on trial for aiding the enemy after passing classified military and State Department files to anti-secrecy website WikiLeaks.

One legal expert was puzzled as to why Snowden fled to Hong Kong, because it has an extradition treaty with the United States while mainland China does not.

In routine criminal cases, unlike this one, Hong Kong had shown a willingness in recent years to extradite people to face charges in the United States, he said.

In the video, Snowden said that "Hong Kong has a strong tradition of free speech."

Hong Kong returned from British to Chinese rule in 1997, but still enjoys some autonomy in business and governmental functions.

Douglas McNabb, a Houston lawyer who specializes in extradition, said it would not be difficult for the United States to provide justification for its request. "This guy came out and said, 'I did it,'" he said. "His best defense would probably be that this is a political case instead of a criminal one."

The treaty would allow Hong Kong to hold Snowden for 60 days while Washington prepares a formal extradition request, but prohibits extradition for political cases.

Jesselyn Radack, a former Justice Department attorney who represents whistleblowers, told Reuters that Snowden had become "one of the most significant leakers ... in U.S. history."

She said she hoped his case could become "a watershed moment that could change the war on whistleblowers and the broader war on information."

Snowden, who said he had left his girlfriend in Hawaii without telling her where he was going, said he knew the risk he was taking, but thought the publicity his revelations had garnered in the past few days had made it worth it.

"My primary fear is that they will come after my family, my friends, my partner. Anyone I have a relationship with," he said. "I will have to live with that for the rest of my life. I am not going to be able to communicate with them. They (the authorities) will act aggressively against anyone who has known me. That keeps me up at night."

He spoke of his willingness to give up a comfortable life in Hawaii, where he earned about $200,000 a year: "I'm willing to sacrifice all of that because I can't in good conscience allow the U.S. government to destroy privacy, Internet freedom and basic liberties for people around the world with this massive surveillance machine they're secretly building."

In the video interview, the bespectacled, lightly bearded Snowden looked relaxed. He said he was ultimately hoping that Iceland, which values internet freedom, might grant him asylum.