The spy agency's watchdog will not comment on whether legislation giving the Security Intelligence Service (SIS) greater powers is being rushed through Parliament too quickly.
Inspector-General of Intelligence and Security Cheryl Gwyn has appeared before the foreign affairs, defence and trade select committee as it goes through its final consideration of the Bill.
Critics of the Countering Terrorist Fighters Legislation Bill say it gives the SIS too much power and is open to abuse.
But Ms Gwyn would not comment before speaking to MPs.
"I'm attending at a private hearing of the committee, at the committee's invitation. I don't have anything to say that I wouldn't be prepared to say publicly" she said.
Reporters were allowed in to hear Ms Gwyn's evidence but were told before she began talking that they could not report what she told the select committee until the Bill is reported back to Parliament tomorrow.
Most reporters left the room.
On another matter, after her appearance, Ms Gywn confirmed she was investigating whether Labour's defence spokesperson Phil Goff leaked parts of her report into the SIS before it was officially released last week.
"And I've invited Mr Goff to discuss it with me...and I'll be making public the outcome of that discussion in due course."
But she refused to say whether she would also investigate the Prime Minister to determine whether he discussed the report in an text message exchange with right-wing blogger Cameron Slater.
SIS director Rebecca Kitteridge also appeared before the committee to answer questions MPs had about the legislation.
On her way in, Ms Kitteridge told reporters it was up to Parliament to decide just what powers the SIS should have.
"My job here is not to advocate particularly for the legislation but to answer factual questions about how the legislation would apply, so it's basically to give them sufficient information about the work of the service so that they can see how the changes would apply in practice."
Meanwhile, the Green Party MP on the committee, Kennedy Graham, said the Greens would not support the Bill no matter what changes were made to it.
"Even if it were not rushed, we don't accept the case that there's a need for expanded state powers pertaining to covert surveillance without warrant by the SIS, when the risk factor has gone from very low, to low."
The Labour Party has indicated it is prepared to vote for the legislation but only as long as substantial changes are made.