The US National Security Agency has tapped into key communications links from Yahoo and Google data centers around the world, the Washington Post reported Wednesday.
The Post, citing documents obtained from former NSA contractor Edward Snowden and interviews with officials, said the program can collect data at will from hundreds of millions of user accounts, including from Americans.
The report said the program dubbed MUSCULAR, operated jointly with NSA's British counterpart GCHQ, indicated that the agencies can intercept data flows from the fiber-optic cables used by the US Internet giants.
The Post report suggests this is a secret program that is unlike PRISM, which relies on court orders to obtain data from technology firms.
According to a top secret document cited by the newspaper dated January 9, 2013, some 181 million records were collected in the prior 30 days, ranging from metadata on emails to content such as text, audio and video.
The document shown by the Post indicates that the NSA intercept takes place outside the United States, and that an unnamed telecommunications provider allowed the secret access.
A graphic in the document suggested that the interception at Google came at a point between the public Internet and Google "cloud" servers.
Acting outside US territory would give the NSA more latitude than within the United States, where it would require court orders, the Post noted.
The NSA, Google and Yahoo did not immediately respond to AFP queries on the report. The Post reported that Google and Yahoo indicated they had not authorized any such access.
NSA chief General Keith Alexander, asked about the allegations during a Washington conference, said he was unaware of the report but argued that the allegations appeared to be inaccurate.
"That (activity) to my knowledge, this never happened," he said.
"In fact there was this allegation in June that the NSA was tapping into the servers of Yahoo or Google, that is factually incorrect."
He added that NSA gains access to data "by court order" and that it would not be "breaking into any databases."
The report comes amid a storm of protest about NSA surveillance both at home and overseas of phone and Internet communications.
On Tuesday, US officials said reports that American spy agencies snooped on millions of Europeans were false.
Alexander told lawmakers that in many cases European spy agencies had turned over phone call records and shared them with US intelligence.