The former CIA contractor who leaked top-secret information about surveillance programs used by American spy agencies has been sacked by the company he worked for.

Edward Snowden, 29, exposed the way the US National Security Agency (NSA) gains information from internet companies as well as US telecoms using a secret program called PRISM.

Mr Snowden travelled from Hawaii to Hong Kong on May 20 carrying a cache of secrets harvested from his employer's servers.

He went into hiding in Hong Kong before leaking the data, and his whereabouts are now unknown.

Contracting company Booz Allen Hamilton has sacked the infrastructure analyst from the job he held for about three months.

What is Booz Allen? A US technology consulting firm that employed Edward Snowden.

A US technology consulting firm that employed Edward Snowden. Clients include the US military, the US Intelligence Community and the Dept of Homeland Security.

Clients include the US military, the US Intelligence Community and the Dept of Homeland Security. The company says it aims to help those clients combat global terrorism and improve cyber capabilities.

The company says it aims to help those clients combat global terrorism and improve cyber capabilities. Mr Snowdon worked for Booz Allen for less than three months and was assigned to a team working in Hawaii.

In a statement posted on its website, the company said it sacked Mr Snowden "for violations of the firm's code of ethics and firm policy".

It has also moved to clarify his salary, saying it was $US122,000, not around $US200,000 as Mr Snowden has claimed.

Mr Snowden has said he chose Hong Kong as a refuge as it has a "strong tradition of free speech".

But the semi-autonomous Chinese region also has an extradition treaty with the Washington, which Beijing may not wish to anger.

Mr Snowden has told the Guardian newspaper he may seek asylum in Iceland.

But the head of Iceland's Directorate of Immigration says it has received no formal request, and Mr Snowden would have to be on Icelandic soil to make one.

The Russian government has said it would consider granting asylum to Mr Snowden, if he were to ask for it.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 2 minutes 45 seconds 2 m 45 s US ramps up rhetoric against Edward Snowden ( Jane Cowan ) Download 1.3 MB

Mr Snowden, who asked the Washington Post and Britain's Guardian newspapers to identify him and his role, says he leaked the information because he believed the United States had built a vast and secret espionage machine to spy on Americans.

"I don't want to live in a society that does these sort of things," he told the Guardian.

"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."

Mr Snowden may yet face severe legal consequences for blowing the lid on Washington's vast snooping program, but he has triggered the public battle he said he wanted.

Who is Edward Snowden? Former CIA contractor who leaked information about US spy agencies

Former CIA contractor who leaked information about US spy agencies He worked for the National Security Agency (NSA) for the last four years

He worked for the National Security Agency (NSA) for the last four years Was employed by various outside contractors, including tech consultancy Booz Allen and computer company Dell

Was employed by various outside contractors, including tech consultancy Booz Allen and computer company Dell He copied secret documents at the NSA office in Hawaii

He copied secret documents at the NSA office in Hawaii He leaked the documents, which expose how the NSA gains information using a secret program called PRISM

He leaked the documents, which expose how the NSA gains information using a secret program called PRISM Says he leaked the data because he was worried about privacy and internet freedom

His revelations launched a broad debate on privacy rights and the limits of security programs in the aftermath of the September 11, 2001, attacks in the United States.

Many members of Congress have expressed support for the surveillance program but have raised questions about whether it should be more tightly supervised and scaled back.

The American Civil Liberties Union, meanwhile, has announced it is suing top US government officials to challenge the validity of the NSA's telephone surveillance program.

The union says it violates rights to free speech and privacy.

The suit, filed in the US District Court of New York, names James Clapper, the director of national intelligence, and the leaders of the NSA, the Defence Department, the Justice Department and the FBI.

ABC/AFP/Reuters