Alleged leaked NATO documents under investigation

(CNN) — The U.S. is investigating a purported leak of classified military documents.

A Pentagon official says what appears to be screenshots of classified U.S. and NATO military information about Ukraine are circulating on social media. The Pentagon Deputy Press Secretary would not weigh in on the documents’ legitimacy.

In a statement he said the defense department is aware of the reports and reviewing the matter. An advisor to the Ukrainian president said he believes Russians are behind the purported leak. Adding that the documents are based on “a large amount of fictitious information.”