They also detail plans to reunite the Korean peninsula after the North's eventual collapse, according to The New York Times, one of a handful of international media outlets that gained early access to the documents.
The cables also detail fresh suspicions about Afghan corruption, Saudi donors financing Al-Qaeda, and the US failure to prevent Syria from providing a massive stockpile of weapons to the Lebanese Hezbollah militia since 2006.
They include closed-door remarks that could stoke scandal, including Yemen's president telling a top US general: "We'll continue saying the bombs are ours, not yours" when discussing secretive US strikes on Al-Qaeda in his country, and a description of Libyan leader Moamer Kadhafi as always being attended by a "voluptuous blonde" Ukrainian nurse.
Most of the 251,287 cables -- many of which are marked "classified" but none "top secret" -- date back to 2007, but the release also includes cables going back as far as 1966, The New York Times said.
The whistle-blower website's chief Julian Assange had earlier described the release as a "diplomatic history of the United States" that would cover "every major issue" as governments braced for damaging revelations.
"We can see already in the past week or so that the United States has made movements to try to disarm the effect that this could have," he said.
The White House slammed the release as a "reckless and dangerous action" that puts lives at risk around the world.
"To be clear -- such disclosures put at risk our diplomats, intelligence professionals, and people around the world who come to the United States for assistance in promoting democracy and open government," White House press secretary Robert Gibbs said in a statement.
The Pentagon, which was infuriated by the website's publication of secret Afghanistan and Iraq war logs earlier this year, also condemned the latest release and unveiled new steps designed to prevent future disclosures.
US officials in recent days have raced to contain the fall-out by warning more than a dozen countries, including key allies Australia, Britain, Canada, Israel and Turkey.
Late on Saturday Washington ruled out negotiating with WikiLeaks, saying it possessed the cables in violation of US law.
US officials said this was in response to a letter Assange had sent to the State Department on Friday in which he had tried to address concerns that the planned release placed individuals at risk.
"As far as we are aware, and as far as anyone has ever alleged in any credible manner whatsoever, no single individual has ever come to harm as a result of anything that we have ever published," Assange said.
The New York Times explained its decision to publish the cables by saying they "serve an important public interest, illuminating the goals, successes, compromises and frustrations of American diplomacy in a way that other accounts cannot match."
The newspaper said it had "taken care to exclude... information that would endanger confidential informants or compromise national security."
It said it had notified White House officials of the cables and asked if further redactions were necessary, adding that it "agreed to some, but not all" of their suggestions.
British officials have said some information might be subject to voluntary agreements between the government and the media to withhold sensitive data governing military operations and the intelligence services.
US officials have not confirmed the source of the leaks, but suspicion has fallen on Bradley Manning, a former army intelligence agent arrested after the release of a video showing air strikes that killed civilian reporters in Iraq.
WikiLeaks argues that the first two document dumps -- nearly 500,000 US military incident reports from 2004 to 2009 -- shed light on the wars in Afghanistan and Iraq.
Sweden recently issued an international warrant for Assange's arrest, saying he is wanted for questioning over allegations of rape and sexual molestation.
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