Citing sources familiar with the investigation, the Washington Post reported Thursday Fox News political correspondent Carl Cameron confirmed to the FBI Shelby told him about sensitive intercepted al-Qaida messages on June 19, 2002, while Shelby was a member of the Senate Select Committee on Intelligence.
Although the FBI and Justice Department have investigated the case and a grand jury was empanelled, no charges have been brought.
Justice is not pursuing criminal charges but has turned the issue over to the Senate Ethics Committee.
In a statement, Shelby's office denied he has ever "knowingly compromised classified information."
The disclosed intelligence reportedly involved two messages intercepted by the National Security Agency just before the Sept. 11, 2001, terrorist attacks, but were not translated until Sept. 12. They were later interpreted as indicating the attacks were about to come.
The leak of the information raised the ire of Central Intelligence Agency and Bush administration officials.