Federal police have been called in to investigate how a draft national security document, which proposed a plan to ramp-up security monitoring of refugees, was leaked to the media.
Immigration secretary Michael Pezzullo confirmed to a Senate estimates hearing on Monday the document was a "pre-exposure draft" prepared internally by his department and circulated to other departments for feedback.
A copy of the document marked "sensitive" proposed new measures to keep extremists out of the country.
Mr Pezzullo would not say how many other departments had access to the document.
Deputy secretary Rachel Noble said a department official discussed the document with one of Immigration Minister Peter Dutton's advisers on January 27, mainly regarding the process and timeframes.
The hearing was told a police inquiry could take a long time because a criminal standard of proof needed to be established.
Public servants who leak government documents can face imprisonment.
