The families of soldiers killed in the Iraq War have threatened to take legal action if a publication date for the Chilcot report is not set within two weeks.
A group of at least 29 families warned inquiry chairman Sir John Chilcot of their intentions in a legal letter, according to The Daily Mail.
The £10 million inquiry finished hearing evidence in February 2011. It was expected to be published ahead of May's general election before being delayed.
Prime Minister David Cameron has demanded a timetable for publishing the long-awaited report be set out "pretty soon". However, Whitehall sources do not expect this to happen before Parliament returns in September.
Sir John insisted last month his inquiry, which was launched in 2009, was making "significant progress" but could not set a date for publication.
He said officials were continuing to work through the so-called "Maxwellisation" process of assessing responses from individuals facing possible criticism in the final report.
ITV News political correspondent Carl Dinnen spoke to Roger Bacon, whose son Major Matthew Bacon, 34, died in a bomb blast in Basra 10 years ago, said the delays were "morally reprehensible".