Israel was briefed by the United States about classified files that were later released by WikiLeaks.
The United States briefed several of its allies on the documents over the weekend. Israel already had been told by the U.S. last week that it could be mentioned in the release of classified U.S. documents.
The WikiLeaks website publishes classified documents from anonymous sources and leaks. It released about 250,000 secret diplomatic cables on Sunday.
"Usually there is a gap between what is said in public and what is said in private, but regarding Israel this gap is not large," Prime Minister Benjamin Netanyahu said Sunday afternoon. "Regarding other countries, the gaps are extremely large."
Netanyahu said he was not told in advance the specifics of what was said in the documents.
State Department legal adviser Harold Koh released a letter to WikiLeaks founder Julian Assange saying that the publication of the documents is illegal and demanding a halt to their publication.
The publication of the documents will "place at risk the lives of countless innocent individuals," ''place at risk on-going military operations" and "place at risk on-going cooperation between countries," the letter reportedly said.
The letter called on WikiLeaks to return the documents to the United States and destroy any copies.