The State Department's top lawyer sent a letter to Assange and his attorney, saying the release threatens global counter-terrorism operations and jeopardizes U.S. relations with its allies.
However, Assange went against the request and said the site will publish hundreds of thousands of documents, which include candid assessments of foreign leaders and governments.
The White House said such initial reporting is "often incomplete information" and doesn't always shape final policy decisions. The White House also called the release "reckless and dangerous" and considers the files to be "stolen."
Wikileaks previously released secret documents related to the wars in Iraq and Afghanistan.
The Associated Press contributed to this report.