While the US National Security Agency (NSA) has partnered with the UK, New Zealand, Canada and Australia under a "Five-Eyes" alliance to share spy information and not spy on each other, new documents show that it secretly planned to do the latter anyway.
A memo, leaked by US whistleblower Edward Snowden and sighted by The Guardian and Channel 4 shows that although the partnership "has evolved to include a common understanding that both governments will not target each other's citizens/persons", sometimes rules need to be broken.
"Under certain circumstances, it may be advisable and allowable to target second party persons and second party communications systems unilaterally, when it is in the best interests of the US and necessary for US national security."
"Second party" refers to countries other than the US in the Five-Eyes alliance.
When such action is deemed necessary, the NSA is required to justify its proposal to spy on its neighbours to the signals intelligence director. If this approval is granted, the "collection, processing and dissemination of the second party information" must remain hidden from the nation being spied on.
Although the memo provides no indication of how often, if at all, this practice is followed, separate leaked documents show that the US has spied on the UK previously.
According to The Guardian, British citizens, even when not under an active investigation, had their mobile phone and fax numbers, emails and IP addresses, had been analysed and retained by the NSA, although these had been "minimised" to remove certain information.
Further documents obtained show that the NSA had procedures in place for how to spy on UK citizens and stated that due to a policy change, it was able to capture and retain unminimised intercepts.
Australia would be one country that the US could have spied on. Its government is currently embroiled in the fallout of revelations that it had tapped the mobile phone calls of the Indonesian president.
Prime minister Tony Abbott has refused to address the claims and said he didn't believe Australia should be expected to apologise. While in Parliament yesterday he acknowledged the embarrassment that the president and Indonesia were experiencing, but blamed the cause of it on media reporting.
The Australian government has not yet addressed the claims that the US, in turn, may have been spying on Australia.
Former Australian Prime Minister Julia Gillard has previously indicated, however, that if her phone had been tapped by the US while she were serving as the country's leader, she would not have been worried.