The Washington Post has published slides from a US National Security Agency presentation detailing processes in the top secret Prism online surveillance system.
The NSA presentation is among the documents leaked by whistleblower Edward Snowden.
The newly released slides give additional details about how Prism operates, including the levels of review and supervisory control at the NSA and FBI.
The slides also show how the programme interacts with top internet companies.
One slide shows what happens when an NSA analyst "tasks" the Prism system for information about a new surveillance target, the paper said.
The slide shows that request to add a new target is passed automatically to a supervisor who reviews the "selectors" or search terms.
The supervisor must endorse the analyst's "reasonable belief" – defined as 51% confidence – that the specified target is a foreign national who is overseas at the time of collection.
According to annotations by the Washington Post, the FBI uses government equipment on private company property to retrieve matching information from a participating company – such as Microsoft or Yahoo – and pass it without further review to the NSA.
A second slide shows how collected data is processed and analysed by specialised systems for voice, text, video and digital network information, including the locations and device signatures of targets.
A third slide shows the Prism case notation format, which indicates the availability of real-time surveillance as well as stored content.
The slide also lists nine “Prism Providers” as Microsoft, Yahoo, Google, Facebook, PalTalk, YouTube, Skype, AOL and Apple, most of which have previously denied giving the NSA access to their systems.
The fourth slide illustrates the scale of the Prism operation, showing that on 5 April 2013 there were 117,675 active surveillance targets in Prism’s counterterrorism database.
The slide does not show how many other internet users, nor among them how many US citizens, have their communications collected "incidentally" during surveillance of those targets.
According to the Washington Post, Prism allows the US intelligence community to gain access from nine internet companies to a wide range of digital information on foreign targets operating outside the US.
Although the programme is court-approved, it does not issue individual warrants, operating instead under a broader authorisation from federal judges, who oversee the use of the US Foreign Intelligence Surveillance Act (FISA).
Revelations of the Prism programme have raised concerns about internet privacy on both sides of the Atlantic and could put a new trade pact between the US and the European Union at risk, according to the Guardian.
Documents leaked by Edward Snowden indicate that the US bugged key EU offices and intercepted phonecalls and emails from top officials, according to the German publication Der Spiegel.
Der Spiegel quoted the Snowden documents as revealing that the US taps half a billion phone calls, emails and text messages in Germany a month.
On an average day, the NSA monitored about 20 million German phone connections and 10 million internet datasets, rising to 60 million phone connections on busy days, the report said.
European Union, German and French officials have called for immediate clarification from the US in light of the concerns raised by the latest revelations about US surveillance.
US authorities have told the European Commission that they are checking the accuracy of the information released at the weekend.
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