The US Secretary of State said she "deeply regrets" the release and attempted to reassure US allies around the world.
"I will not comment on or confirm what are alleged to be stolen State Department cables," Mrs Clinton said.
"But I can say that the United States deeply regrets the disclosure of any information that was intended to be confidential, including private discussions between counterparts or our diplomats' personal assessments and observations.
"I want to make clear that our official foreign policy is not set through these messages, but here in Washington," Mrs Clinton added. "Our policy is a matter of public record as reflected in our statements and our actions around the world.
"I would also add that to the American people and to our friends and partners, I want you to know that we are taking aggressive steps to hold responsible those who stole this information," she said.
American politicians have reacted with fury at WikiLeaks, calling on the group to be designated a "Foreign Terrorist Organisation" and calling on President Barack Obama to pursue a prosecution.
Senator John Kerry of Massachusetts, chairman of the Senate Foreign Relations Committee and also a Democrat, branded the leaks a "reckless action which jeopardises lives by exposing raw, contemporaneous intelligence".
Senator Joe Lieberman, an Independent, described the leaking as "an attack on the national security of the United States" and an "outrageous, reckless, and despicable action" that would leave those responsible with "blood on their hands".
Representative Peter King of New York, a long-time supporter of Sinn Fein, the political wing of the IRA, called on Hillary Clinton, the US Secretary of State, to designate WikiLeaks a "Foreign Terrorist Organisation" outlawed in the US.
"WikiLeaks presents a clear and present danger to the national security of the United States. I strongly urge you to work within the Administration to use every offensive capability of the U.S. government to prevent further damaging releases by WikiLeaks," he said in a statement.
Senator Lindsay Graham of South Carolina, a Republican, told Fox News: "People who do this are low on the food chain as far as I'm concerned. If you can prosecute them, let's try."
His Democratic colleague Senator Claire McCaskill of Missouri agreed with him and said she hoped "we can find out where this is coming from and go after them with the force of law". She added that "the people who do these document leaks need to do a gut check about their patriotism".
The Pentagon blasted WikiLeaks for its "reckless" dump of classified documents and said it was taking steps to bolster security of classified U.S. military networks.
Minutes after the documents were published, the White House issued a statement trying to play down the contents of the documents.
"By its very nature, field reporting to Washington is candid and often incomplete information. It is not an expression of policy, nor does it always shape final policy decisions."
But it made clear the documents were authentic and damaging. "Nevertheless, these cables could compromise private discussions with foreign governments and opposition leaders, and when the substance of private conversations is printed on the front pages of newspapers across the world, it can deeply impact not only US foreign policy interests, but those of our allies and friends around the world.
