"It’s not in the public interest for the AFP to answer the question on the grounds that it may prejudice the ongoing investigation of a possible breach of law,"the deputy commissioner said under questioning by Labor senator Murray Watt.
Ms Close said dozens of people had been interviewed during the investigation,but refused to say if government ministers including Senator Cash had assisted police.
It emerged last week that the AFP planned to refer part of its investigation into the leaks to the Commonwealth Director of Public Prosecutions.
Opposition employment spokesman Brendan O'Connor said Senator Cash"must explain whether the AFP has sought to interview her,whether she has participated in such an interview and whether she has co-operated with the investigation".
"It is in the public interest to know if the AFP is investigating the role of the minister and her office in the leak and Senator Cash should come clean,"Mr O'Connor said.