David Cameron has told told the head of the inquiry into the Iraq war he is "disappointed" that the findings will not be published until next summer and urged him to "expedite" the final stages.
Sir John Chilcot announced earlier that his team expects to complete the text of its two million word report by the week commencing April 18 and aims to publish it by June or July 2016.
But in a letter to the inquiry chairman, the Prime Minister said the families of those who served in Iraq would share his disappointment at the timescale.
He wrote: "I recognise that you have a significant task, but would welcome any further steps you can take to expedite the final stages of the inquiry."
Sir John said the report would be made available to officials for "national security checking" and preparation for publication once it is completed.
The process is required to ensure the Government's obligations under the European Convention on Human Rights and the protection of UK national security "will not inadvertently be breached by publication of the inquiry's report as a whole", he said.
But the Prime Minister pointed out the Saville Inquiry into Bloody Sunday took just two weeks to complete and said he expected the process for the Iraq report to "take no longer than this".
He added: "Whilst it is welcome of course that there is now a clear end in sight for your inquiry, I am disappointed - and I know the families of those who served in Iraq will also be disappointed - that you do not believe it will be possible logistically to publish your report until early summer."
Tony Blair, who ordered the original invasion of Iraq in 2003, appeared before the inquiry twice.
Although the probe looked at the entire period of British operations in Iraq, much of the focus has been on the decision to overthrow Saddam Hussein.
Sir John, however, has always said he would not deliver a verdict on whether the conflict was lawful or not.
Critics have claimed Mr Blair is partly responsible for the delays in publication through the Maxwellisation process that gives witnesses a chance to respond to criticism before the findings are released - a claim the former prime minister has again strongly denied.
A spokesman for Mr Blair said: " Tony Blair has always wanted the inquiry to report as soon as it properly can and he looks forward to responding to the inquiry's report.
"Mr Blair also wants to make it clear that the timetable of the inquiry and the length of time it will have taken to report is not the result either of issues over the correspondence between him as Prime Minister and (US) President Bush, or due to the Maxwellisation process.
"As for the first, the correspondence has been with the inquiry from the beginning. The only question was over how much of the correspondence could be published in the final report, not about its content being used to inform the report. In any event that question was resolved between the Cabinet Office and the inquiry in May 2014.
"Secondly, Tony Blair received the deliberations of the inquiry under the Maxwell process in full only in January 2015, four years after the inquiry finished taking evidence. He responded by August. This is not therefore the reason for the delay, as Sir John Chilcot has made clear.
"It is our understanding that other witnesses also received information very late in the process, so any suggestion that witnesses have been the cause of the delay is categorically incorrect and this has again been stated clearly and publicly by Sir John."
The announcement of a timescale for publication comes amid increasing frustration among politicians and the families of service personnel who lost their lives in the conflict at the long delay in completing the report.
Mr Cameron has previously described the hold-ups - which mean it should finally be released some seven years after the inquiry was first launched - as "extremely frustrating".
Sir John has blamed a lengthy dispute with the Civil Service over the declassification of official documents as well as a need to give individuals facing criticism the chance to respond.
The "lessons learned" inquiry was first announced by then prime minister Gordon Brown in June 2009 and began public hearings in November of that year.
In the course of the inquiry, it took evidence from politicians, generals, civil servants and intelligence chiefs.
Mr Cameron said he would publish the findings as quickly as possible after they finally land on his desk.
During a press conference for the Northern Future Forum in Reykjavik, Iceland, he said: "I'm immensely frustrated by the slowness and the amount of time it has taken.
"I'm not frustrated on my own behalf, I'm frustrated for the mums and the dads who lost loved ones and who want to know what happened and why it happened and want to make sure that the lessons are learnt.
"What I can say is this is an independent inquiry, the timing is not set by the Government. Indeed, if the last Labour government had started this inquiry when my party first put it forward in parliament this inquiry, even on this elongated timetable, would have been done and dusted and read and absorbed by now.
"What I can say for my own part is that as soon as this report arrives on my desk I will move as quickly as I possibly can to publish it, as I did with the Saville Inquiry into Bloody Sunday, where it was published, I think, within two weeks.
"But, I share the frustrations of many across our country. We should be learning the lessons of what happened. It shouldn't have taken this long."