The US National Security Agency has used a unique, decades-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 New York Times said it was unclear whether the programs 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 travelled through its domestic networks, and helped the spy agency wiretap all online communications at United Nations headquarters, the documents suggest.
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 said.
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 fibre optic cable damaged during the 2011 Japan earthquake, for example, was repaired on the same date as an AT&T cable.
The program spied on the UN headquarters internet line in response to an order by the special US Foreign Intelligence Surveillance Court, the documents say.