Whistleblowing website WikiLeaks has published top secret documents which they claim show the US intercepted private communications between German chancellor Angela Merkel and UN Secretary General Ban-Ki Moon.

The recently released documents also claim to show America's National Security Agency (NSA) listened in on exchanges between other allied heads of state and the UN refugee agency.

One of the phone conversations apparently recorded by the NSA was between Israeli prime minister Benjamin Netanyahu and former Italian prime minister Silvio Berlusconi, in which the two allied leaders discussed how Italy could help repair Israel's relationship with the US in 2010.

They reportedly also listened in on an account of a 2011 meeting between Merkel, Berlusconi and former French president Nicolas Sarkozy, which was described by Berlusconi's personal adviser Valetino Valentini.

Valentini apparently said the meeting was "tense and very harsh toward the Rome government," and claimed Sarkozy told Berlusconi that the Italian banking system could "pop like the cork in a champagne bottle" if he didn't bring in "strong, concrete" measures to remedy Italy's debt problem.

The intercepted conversation between Ban Ki-moon and Merkel, which took place in 2008, was apparently about how the EU would show strong leadership in the UN climate conference in Poznan.

WikiLeaks editor and founder Julian Assange, who has been living in the Ecuadorian Embassy in London since 2012, said the bugging showed the US was "intent on protecting its largest oil companies" ahead of the climate meeting.

The WikiLeaks releases also claim to show that the NSA targeted representatives of the UN refugee agency for bugging, and listened in on conversations about secret World Trade Organisation issues between Japanese and EU trade ministers.

These recent leaks are not the first which claim to show that the US spied on allied EU leaders. In June last year, the French government called the practice "unacceptable" after WikiLeaks revealed the US had bugged the phones of the country's last three presidents.

President Francois Hollande later called President Barack Obama to demand guarantees that US spy agencies were no longer listening to his private conversations.