An internal audit by the U.S. National Archives has found that thousands of documents already in the public domain were re-classified in a secret agreement with U.S. government departments.
The audit found that 25,000 government documents have been re-classified since the 1990s. It found that one-third of them did not contain information sensitive enough to be re-classified as secret.
The investigation found that the U.S. Air Force and the Central Intelligence Agency had requested the re-classification of most of the documents.
National Archives head Allen Weinstein has promised transparency and consistent standards in any future re-classifications.
Historians who use the Archives were the first to discover that documents already in the public domain had been removed from view. They alerted Archives officials who ordered the audit.
The Archives are the nation's chief historical repository and contain records including the 1776 Declaration of Independence and the U.S. Constitution, as well as recently de-classified documents.
Some information for this report was provided by AFP, AP and Reuters.