Between 2003 and 2009, 179 British service personnel were killed in Iraq
Ministers, civil servants and senior military figures will be expected to give evidence to the Iraq war inquiry in public, its chairman has said.
Only "genuine" issues of national or personal security should prevent them from doing so, Sir John Chilcot said.
His remarks came as the inquiry said it would hold its first public hearings next month in London, although details of witnesses have yet to be released.
Opposition parties have insisted all proceedings should be in public.
Gordon Brown has said it is up to Sir John to decide the format of the inquiry but has indicated he would be willing to appear in public.
The prime minister, his predecessor Tony Blair and Jack Straw, foreign secretary at the time of the 2003 invasion, are among those expected to be called to give evidence.
"Ministers, senior military officers, members of the senior civil service and their equivalents and former holders of those posts should all expect to give evidence in public," Sir John said.
"Only if there are genuine issues of national or personal security would such senior witnesses be justified in seeking to give some of their evidence in private."
The inquiry will hold its first public hearings on November 24 at the QEII conference centre in central London.
Earlier this month, the committee met the families of personnel killed in Iraq and serving officers.