They include reports of some Arab leaders - including the Saudi king - urging the US to attack Iran and end its nuclear weapons programme.
Other concerns include the security of Pakistani nuclear material that could be used to make an atomic weapon.
The widespread use of hacking by the Chinese government is also reported.
The leaked US embassy cables also reportedly include accounts of:
* Corruption within the Afghan government, with concerns heightened when a senior official was found to be carrying more than $50m in cash on a foreign trip
* Bargaining to empty the Guantanamo Bay prison camp - including Slovenian diplomats being told to take in a freed prisoner if they wanted to secure a meeting with President Barack Obama
* The extraordinarily close relationship between Russian PM Vladimir Putin and his Italian counterpart Silvio Berlusconi
* Alleged links between the Russian government and organised crime
* American and South Korean officials' discussions about the prospects for a unified Korea should North Korea collapse as a viable state
* Sharply critical accounts of UK military operations in Afghanistan
The US government has condemned the release of state department documents.
"President Obama supports responsible, accountable, and open government at home and around the world, but this reckless and dangerous action runs counter to that goal," a White House statement said.
"We condemn in the strongest terms the unauthorised disclosure of classified documents and sensitive national security information."
The founder of Wikileaks, Julian Assange, says the US authorities are afraid of being held to account.
Earlier, Wikileaks said it had come under attack from a computer-hacking operation.
"We are currently under a mass distributed denial of service attack," it reported on its Twitter feed.
No-one has been charged with passing the diplomatic files to the website but suspicion has fallen on US Army private Bradley Manning, an intelligence analyst arrested in Iraq in June and charged over an earlier leak of classified US documents to Mr Assange's organisation.
Wikileaks argues that the site's previous releases shed light on the wars in Afghanistan and Iraq.
