The cables were sent by US ambassadors, and those published so far cover topics ranging from the authorities encouraging spies to track UN delegates, to Middle Eastern nations encouraging military action against Iran.

Major companies have also been targeted this week, with oil giant it had staff in every major ministry of the Nigerian government, where its business has come under criticism, and drugs firm Pfizer reportedly hiring private investigators to run a smear campaign that could help about trials of its drugs on African children.

Both companies deny the accusations.

A poster for the plan urges hackers to "post snippets of the leaks everywhere", including on fan forums, news sites and YouTube videos. Anonymous spokespeople have not officially claimed responsibility for the plan.