WASHINGTON (AFP) - The United States National Security Agency (NSA) has used a unique, deades-old partnership with AT&T to snoop on Internet usage, according to newly disclosed documents leaked by Edward Snowden.

The documents provided by the former NSA contractor and reviewed by The New York Times and ProPublica described a "highly collaborative" telecom giant that demonstrated an "extreme willingness to help".

The Times said it was unclear whether the programmes are still operational in the same way today. The documents were dated from 2003 to 2013.

AT&T granted the NSA access to billions of emails that traveled through its domestic networks, and helped the spy agency wiretap all online communications at United Nations headquarters, the documents show.

AT&T has provided the Internet line to the world body's headquarters.

Company spokesman Brad Burns insisted that "we do not provide information to any investigating authorities without a court order or other mandatory process other than if a person's life is in danger and time is of the essence".

"For example, in a kidnapping situation we could provide help tracking down called numbers to assist law enforcement," he told AFP.

In the documents, AT&T and other companies are not identified by name but rather codenamed.

One of the oldest programs, Fairview, was launched in 1985 and involves AT&T, the Times and ProPublica said, citing several former intelligence officials.

A Fairview fiber optic cable damaged during the 2011 Japan earthquake, for example, was repaired on the same date as an AT&T cable.

The programme spied on the UN headquarters Internet line in response to an order by the special US Foreign Intelligence Surveillance Court, the documents show.

Washington has since told the UN it would not collect data on its communications.

Verizon and the former MCI - which Verizon purchased in 2006 - are part of another program, codenamed Stormbrew.

AT&T began providing to the NSA some 1.1 billion domestic cellphone calling records a day in 2011, after a "push to get this flow operational prior to the 10th anniversary of 9/11", the newly released documents showed.

That same year, the NSA spent US$188.9 million on Fairview, more than twice the amount on the next-largest corporate programme, Stormbrew.

Intelligence officials had initially said that the phone calls the NSA had collected were mostly from landline, not cellular, phone records, after Snowden first revealed the wiretapping programme.