Top-secret US intelligence documents leaked by whistleblower Edward Snowden have revealed details of a key signals intelligence program used by the Australian intelligence community to harvest internet and telecommunications traffic across the Asia-Pacific region.

The system known as X-Keyscore allows the US National Security Agency and international partners including Australia to monitor ''nearly everything a typical user does on the internet'', according to the leaked documents published by Britain's Guardian newspaper.

X-Keyscore: Allows the NSA and allies to monitor emails, web browsing, internet searches and social media. Credit:Mayu Kanamori/Jessica Hromas

According to classified intelligence training materials, X-Keyscore allows the NSA and its allied partners to comprehensively monitor the emails, web browsing, internet searches and social media use of targets.