The US intelligence agency is said to have spied on leaders at the 2009 Copenhagen Climate change summit in an effort to gain strategic advantage on the decision-making process.

A top secret National Security Agency (NSA) document from whistleblower Edward Snowden, published jointly by the Huffington Post and the Danish daily newspaper Information on Wednesday (29 January), reveal the so-called “Five Eyes” snooping club of English-speaking nations were working together to spy on other government’s leaders and policy-makers at the summit.

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The documents notes that “analysts here at NSA, as well as our second party partners, will continue to provide policymakers with unique, timely, and valuable insights into key countries' preparations and goals for the conference, as well as the deliberations within countries on climate change policies and negotiation strategies.”

Second party partners refer to intelligence agencies from the United Kingdom, Canada, Australia, and New Zealand.

The two-week summit - US president Barack Obama's first climate change meeting - was billed as a major event aimed to cut global CO2 emissions but ended up as a five-page non-binding agreement seen as a victory for rich industrialised nations.

NSA-led signals intelligence, which intercepts telephone calls and emails, was used to “play a significant role in keeping our negotiators as well informed as possible throughout the 2-week event,” notes the document.

The information was then fed to US negotiators to keep them clued in on “intense last-minute policy formulating” as well as on side-discussions among and between other climate representatives.

The US is not alone in snooping on leaders at summits.

The Guardian newspaper last June reported that the UK’s GCHQ set up fake internet cafes and intercepted telephone communications of foreign leaders at two G20 summit meetings in London in 2009.

Obama earlier this month in a speech said he would not spy on leaders considered to be close allies "unless there is a compelling national security purpose.”

But the steady stream of revelations since last June has since eroded EU trust towards the US.

In a speech to the German Bundestag on Wednesday, German Chancellor Angela Merkel criticised the scope of US intelligence gathering.

"Can it be right that in the end it isn't about defence against terrorism but about, for instance, gaining advantages over allies in negotiations at G-20 summits or United Nations meetings? Our answer can only be 'no', that can't be right," she said.

But the chancellor said the US would remain a close ally and a strategic partner, despite the revelations.