NEW YORK (AFP) –- U.S. intelligence agencies have been removing from public access thousands of historical documents that were available for years, including some already published or obtained by private historians, The New York Times reported Tuesday.

The newspaper said the restoration of classified status to more than 55,000 previously declassified pages began in 1999, when the Central Intelligence Agency and five other agencies objected to what they saw as a hasty release of sensitive information.

It accelerated after the administration of President George W. Bush took office and especially after the 2001 terrorist attacks, according to the report.

But because the reclassification program is itself shrouded in secrecy, it continued virtually without outside notice until December, the paper said.

That was when an intelligence historian, Matthew Aid, noticed that dozens of documents he had copied years ago had been withdrawn from the archives' open shelves.

Those included mostly decades-old State Department reports from the Korean War and the early Cold War, The Times said. He found that eight reclassified documents had been previously published in the State Department's history series, "Foreign Relations of the United States."

"The stuff they pulled should never have been removed," the paper quoted the historian as saying.

"Some of it is mundane, and some of it is outright ridiculous."

After Aid and other historians complained, the archives' Information Security Oversight Office began an audit of the reclassification program, according to The Times.