(CNN) -- If any materials in the next posting of documents by the WikiLeaks site were provided by government officials without proper authorization, "they were provided in violation of U.S. law and without regard for the grave consequences of this action," the U.S. State Department's legal adviser said.
In a letter to WikiLeaks founder Julian Assange dated Saturday, State Department Legal Adviser Harold Hongju Koh said he was responding to a letter about plans to publish "what you claim to be classified U.S. government documents."
Koh wrote that the department had spoken with representatives from The New York Times, The Guardian and Der Spiegel newspapers about 250,000 documents the whistleblower organization provided to them for publication.
He described the distribution as the "illegal dissemination of classified documents" and said it would "place at risk the lives of countless individuals" -- criticisms that have been repeated by U.S. officials after past postings on the site.
The information blitz from WikiLeaks is expected to offer a glimpse into the worldwide communications of the State Department and its 297 embassies, consulates and missions through what commonly are referred to as "cables."
Koh wrote that releasing such documents could jeopardize relationships with allies, military actions and anti-terrorism operations.
WikiLeaks indicated last week that it was preparing to release a new batch of previously classified U.S. military documents.
"Next release is 7x the size of the Iraq War Logs," the group stated via Twitter Monday. "Intense pressure over it for months. Keep us strong."
CNN has not had advanced access to the documents, unlike some media organizations, because the company declined to sign a confidentiality agreement with WikiLeaks.
In October, WikiLeaks released nearly 400,000 U.S. military reports about operations in Iraq. In July, it released more than 70,000 reports from the war in Afghanistan.
CNN Senior State Department Producer Elise Labott contributed to this report.