WASHINGTON: The US National Security Agency has monitored hundreds of millions of email and instant messaging accounts around the world, The Washington Post reported on Tuesday.

The NSA’s monitoring systems focus on data crucial to government security in the United States and in allied nations, the report added.

The Post based its report on information it received from senior intelligence officials and on top secret documents provided by former NSA contractor Edward Snowden.

The agency also monitors “tens of millions” of US citizens although privacy laws prevent the US government from spying on its own citizens, the report claimed.

The majority of the contacts come from Yahoo and Hotmail accounts, but others also come from Facebook, Google and unspecified other providers. The contacts amount to a sizeable portion of the world’s email and instant messaging accounts.

“You need the haystack to find the needle,” NSA Director Gen. Keith B. Alexander told the Post while defending his agency’s massive monitoring programme.

The Post quoted senior US intelligence officials as saying that such collection would be illegal if done from facilities in the United States.

The NSA, however, has avoided that error by intercepting contact lists from points “all over the world”, one anonymous official told the newspaper.

Large technology companies use data centres around the world to ease the loads on their servers in the United States.

But all major service providers — Google, Microsoft, Facebook and Yahoo — told US media outlets that they were neither aware of nor had participated in any mass collection of user data by the US government.

The American Civil Liberties Union called the programme a breach of Americans’ basic rights.

The programme intercepts email address books and “buddy lists” from instant messaging services as they move across global data links. It gathers contact lists in large numbers and analyses data to search for hidden connections and to map relationships.

During a single day last year, the NSA’s Special Source Operations branch collected 444,743 email address books from Yahoo, 105,068 from Hotmail, 82,857 from Facebook, 33,697 from Gmail and 22,881 from unspecified other providers. Those figures, described as a typical daily intake in the document, correspond to a rate of more than 250 million a year.

Each day the agency collects contacts from an estimated 500,000 buddy lists on live-chat services as well as from the inbox displays of Web-based email accounts.

Foreign telecommunications companies and allied intelligence services cooperate with the NSA in collecting this data.

Contact lists stored online provide the NSA with far richer sources of data than call records alone. Address books commonly include not only names and email addresses, but also telephone numbers, street addresses, and business and family information. Inbox listings of email accounts stored in the “cloud” sometimes contain content, such as the first few lines of a message.

Taken together, the data can be used to draw detailed maps of a person’s life, as told by personal, professional, political and religious connections.

The NSA has not been authorised by Congress or the special intelligence court that oversees foreign surveillance to collect contact lists in bulk.

Because of the method employed, the agency is not legally required or technically able to restrict its intake to contact lists belonging to specified foreign intelligence targets.