WikiLeaks has released "highly classified documents" that reportedly reveal how the US' National Security Agency (NSA) spied on world leaders, including the United Nations Secretary General Ban Ki-Moon. The documents leaked on 23 February state that world leaders Angela Merkel, Benjamin Netanyahu, Silvio Berlusconi and Nicolas Sarkozy were spied on.

WikiLeaks has noted that some of the released documents are classified as "top secret/comint-gamma" and has cited them as being "the most highly classified documents ever published by a media organisation". The documents state that the NSA listened into high-level meetings on climate change, economics, and even a conversation in which Italy's Berlusconi promised to help Netanyahu in "mending damaged relationships with the US".

WikiLeaks editor Julian Assange said: "Today we showed that UN Secretary General Ban Ki-Moon's private meetings over how to save the planet from climate change were bugged by a country intent on protecting its largest oil companies. We previously published Hillary Clinton's orders that US diplomats were to seal the secretary general's DNA. The US government has signed agreements with the UN that it will not engage in such conduct against the UN – let alone its secretary general."

Among the leaked documents is one that appears to intercept communication between Japanese and German diplomats, in which they reveal plans regarding climate change negotations at the G8 summit in Copenhagen 2009. In Ban Ki-Moon's conversation with Merkel, the secretary general said that the new US administration "will have a very engaging and proactive attitude on the issue", making it the right time for the EU to "create conditions necessary for reaching a meaningful deal" at the 2009 UN Climate Talks.

RELEASE: NSA intercepts of UN Sec Gen Ban KiMoon, Merkel, Netanyahu, Sarkozy & Berlusconi https://t.co/XbwyNSwTXg pic.twitter.com/ZpsX5JowXv — WikiLeaks (@wikileaks) February 23, 2016

The document also revealed that Merkel thought the tough issue would be dealing with carbon dioxide trading and that both wanted to host a "mini-summit" in early 2009 that would give them a "clear idea of US intentions". The WikiLeaks release noted that Merkel did not think a climate change deal would be made if not discussed at the heads-of-state level.

Assange said: "It will be interesting to see the UN's reaction, because if the secretary general can be targeted without consequence then everyone from world leader to street sweeper is at risk."

Another document published by WikiLeaks stated that Netanyahu had asked European leaders for help in "smoothing out the rift" in relations with the UN, following the announcement of plans to build 1,600 housing units in northern Jerusalem in 2010. According to the document, Netanyahu believed that the rift had been caused due to "the absence of direct contact between himself and the US president".

The document added that Netanyahu said the objective was to "keep the Palestinians from using this issue as a pretext to block a resumption of talks or to advance unrealistic claims that could risk sinking the peace negotiations altogether".