A U.S. Justice Department report concluded tactics agents considered ineffective and possibly illegal remained in use, even though FBI agents passed along concerns to White House senior staff members, The Washington Post reported Wednesday.

The audit, released Tuesday, included an instance in 2003 in which U.S. Attorney General John Ashcroft reportedly voiced concerns about the Pentagon's strategy for one detainee with national security adviser Condoleezza Rice.

Nearly half of the 450 FBI agents at Guantanamo reported seeing or hearing about military interrogators using tactics such as sleep deprivation and short-shackling. The techniques were used before they were approved, possibly violating Pentagon policy and U.S. law, the report said.

"Some have suggested that the abuse of detainees in U.S. custody was simply the result of a few bad apples acting on their own," said Sen. Carl Levin, D-Mich. , chairman of the Senate armed Services Committee. "The report ... is proof that that is simply not true."

The audit relied on e-mail and memos for its account of tactics the government used against suspected terrorists after the Sept. 11, 2001, attacks, the Post said.