The man leading an inquiry into Britain's role in the Iraq war says he can't estimate when his long-delayed report might be published.

John Chilcot was pressed by a committee of lawmakers about the publication date for his report. He began his inquiry in 2009 and heard from the final witness in 2011.

Last month Chilcot conceded that his report would not be published before Britain's national election in May.

On Wednesday he said "it's impossible to say" when it would be ready and he didn't want to raise false hopes.

The release was initially stalled by wrangling over the inclusion of classified material, including conversations between then-Prime Minister Tony Blair and President George W. Bush.

It is being further delayed to give individuals it mentions a chance to respond.