The Bush administration told Congress yesterday it will investigate whether one-time ally Mr Ahmad Chalabi undermined US security.
Government officials said Mr Chalabi was alleged to have told Iran that the United States had broken secret communication codes used by Tehran's spy service.
US officials said the FBI was also investigating who leaked top secret information to the former Iraqi exile that allegedly was given to Iran.
The FBI has begun administering polygraph examinations on a small number of Pentagon employees who had access to the information that was comprised, the New York Timesreported today.
Mr Chalabi has denied he turned over US secrets to Iran. Yesterday, his lawyers released a letter they said had been sent to Attorney General John Ashcroft and FBI Director Robert Mueller repeating Mr Chalabi's denials, the Timesreported.