A 29-year-old American who works as a contract employee at the National Security Agency (NSA) is the source of The Guardian's disclosures about the US government's secret surveillance programmes, the newspaper has reported.
The leaks have reopened the post-9/11 debate about privacy concerns versus heightened measures to protect against terrorist attacks, and led the NSA to ask the Justice Department to conduct a criminal investigation.
"I have no intention of hiding who I am because I know I have done nothing wrong," Mr Snowden was quoted as saying.
The director of national intelligence, James Clapper, has decried the revelation of the intelligence-gathering programmes as reckless, and in the past few days has taken the rare step of declassifying some details about them to respond to media reports about counter-terrorism techniques employed by the government.
An internet scouring programme codenamed Prism allows the NSA and FBI to tap directly into the servers of major US internet companies such as Google, Apple, Microsoft, Facebook and AOL, scooping out emails, video chats, instant messages and more to track foreign nationals who are suspected of terrorism or espionage.
The NSA is also collecting the telephone records of millions of American customers, but not actual conversations.
Mr Snowden is quoted as saying that his "sole motive is to inform the public as to that which is done in their name and that which is done against them".
The Guardian reported that Mr 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.