The web of information collected by the National Security Agency is even larger than previously thought, with The Washington Post reporting that the agency is collecting hundreds of millions of contact lists from personal email and instant messaging accounts worldwide -- including those of many Americans.
The newspaper said the information came from secret documents provided by NSA leaker Edward Snowden that was confirmed by senior intelligence officials.
The NSA, in a statement issued Monday night, did not deny the claim, but claimed it was not seeking personal details from most Americans.
"The National Security Agency is focused on discovering and developing intelligence about valid foreign intelligence targets like terrorists, human traffickers and drug smugglers," the statement said.
"We are not interested in personal information about ordinary Americans. Moreover, we operate in accordance with rules approved by either the Attorney General or the Foreign Intelligence Surveillance Court, as appropriate, designed to minimize the acquisition, use, and dissemination of any such information."
The program is designed to monitor relationships and conversations to detect links to terrorism or other criminal activity. It allows the NSA to gather contact lists in large quantities rather than target users one by one.
The Post reported that according to an internal NSA PowerPoint, the agency collected 444,743 email address books from Yahoo, 105,068 from Hotmail, 82,857 from Facebook, 33,697 from Gmail and 22,881 from other providers in just one day in 2012.
The presentation said this day represents a typical day for the agency, meaning the data is collected at a rate of more than 250 million per year.
The data collection takes place overseas but includes millions of Americans, sources told the Post.
The Post reported that contact lists can allow NSA analysts to create a detailed map of a person's life and social connections. The information provides a much clearer picture of the individual than merely collecting their phone records, since it can reveal a person's political, professional and religious affiliations as well.
The NSA has not received permission to collect contact lists in bulk, and it is illegal to do so from the U.S. However, sources told the Post the agency gets around this restriction by collecting the data from different locations worldwide.
Previous leaks by Snowden, a former NSA systems analyst, have revealed the bulk collection of millions of U.S. phone among other secret NSA activities.
The revelations have prompted privacy activists and lawmakers to push for an ongoing review of the Foreign Intelligence Surveillance Act, which allows such data collection.
The Associated Press contributed to this report.