Gen Sir John Reith gave evidence in private for "personal reasons"
The Iraq Inquiry met behind closed doors to hear evidence from the general who ran the British operations in the conflict, it has emerged.
Gen Sir John Reith said he should be allowed to appear without the press and public present "for personal reasons".
A full transcript of his evidence was published with five words blanked out, which the inquiry said was on "national security" grounds.
The panel said this was "unrelated" to the hearing being held in private.
However, it gave no further details.
Although Sir John Chilcot, who leads the panel, has pledged to hear as much evidence in public as possible, the committee said it decided that the personal grounds laid out by Gen Reith meant "there was a genuine reason why he would have difficulty appearing in public if it were to be broadcast".
Earlier in the week Tony Blair's ex-spokesman Alastair Campbell appeared before the panel and told the inquiry he "defends every single word" of the 2002 dossier on Iraq's weapons of mass destruction.
He said parts could have been "clearer" but it did not "misrepresent" Iraq's threat.
The inquiry is set to adjourn ahead of the general election campaign.
Prime Minister Gordon Brown and Foreign Secretary David Miliband are among those set to appear before the inquiry after the election.
However, Mr Brown has faced calls to give evidence to before the election.
Tony Blair's appearance
Liberal Democrat leader Nick Clegg said people were "entitled" to know the prime minister's role in the decision to go to war before voting, since Mr Brown was the chancellor at the time and had therefore "signed the cheques".
The Conservatives also said it would be "preferable" for him to give evidence to the inquiry before the election, rather than afterwards.
However, the prime minister told MPs he was acting on the inquiry's recommendations over timings and said he "stood by" the decision to go to war.
Former Defence Secretary Geoff Hoon and former Foreign Secretary Jack Straw will give evidence to the inquiry next week with former Prime Minister Tony Blair expected to appear at a later date.
The Iraq Inquiry's final report is due to be published by early next year.