Media playback is unsupported on your device Media caption Sir John Chilcot said he was "disappointed" by Cabinet Secretary Gus O'Donnell's decision

The government has refused to release "key extracts" of some conversations between George Bush and Tony Blair relating to the Iraq war.

Iraq Inquiry Chairman Sir John Chilcot said he was "disappointed" by Cabinet Secretary Gus O'Donnell's decision to keep "important" documents secret.

But Sir Gus said it would not be "in the public interest" to release them.

Sir John's panel has seen the classified documents but is not being allowed to make them public.

Downing Street said Prime Minister David Cameron had played "no role" in the decision.

Letters released by the inquiry outline the dispute between Sir John and Sir Gus over the release of notes sent from Mr Blair to Mr Bush and of the details of recorded conversations between the two former leaders.

They were published as Sir John's five-member panel resumed its public hearings after a break of almost six months. Mr Blair is set to give evidence for a second time on Friday.

'Inhibiting'

In his correspondence with Sir John, the cabinet secretary said "exchanges between the former UK Prime Minister and US President represent particularly privileged channels of communication, the preservation of which is strongly in the public interest".

He added: "Even where immediate severity may have passed, disclosure of the material could still prejudice relations by inhibiting future exchanges.

Analysis Sir John Chilcot's opening statement reflected both disappointment and frustration with the government for failing to publish the exchanges between Tony Blair and George W Bush. It is not the first time that the failure to declassify key documents has been a source of irritation to members of the Iraq Inquiry. A year ago, when the former Attorney General, Lord Goldsmith, was giving evidence, both he and the committee were frustrated that not all the relevant documents had been declassified at the time. Then, as now, the committee had been able to see all the papers itself, but not allowed to refer to them during public hearings because the documents were not in the public domain. It appears the Cabinet Office is worried that the publication of the Blair-Bush exchanges, could set an unwelcome precedent.

"A UK prime minister may be less likely to have these exchanges (or allow them to be recorded) if he is concerned that this information would be disclosed at a later time against his wishes."

But, in his opening comments to the inquiry session, Sir John said he had asked for permission to release the documents in December and had promised Sir Gus that, if this was not granted, he would publish their correspondence.

He said: "The papers we hold include the notes which Prime Minister Blair sent to President Bush and the records of their discussions.

"The inquiry recognises the privileged nature of those exchanges but, exceptionally, we sought disclosure of key extracts which illuminate Prime Minister Blair's positions at critical points. The Cabinet Office did not agree this disclosure."

Sir John added: "The inquiry is disappointed that the cabinet secretary was not willing to accede to its request. This means that in a narrow but important area the inquiry may not always be able to publish as fully as it would wish the evidential basis for some of its comments and conclusions.

"The inquiry is free to say what it thinks. We shall complete our task and make our own independent judgements about the UK's involvement in Iraq."

In a letter to Sir Gus, he highlighted the fact that Mr Bush and Mr Blair - as well as the former prime minister's chief of staff Jonathan Powell and communications chief Alastair Campbell - had revealed details of some of their talks in recent memoirs,

He also said the inquiry's agreed protocol on releasing documents supported disclosure.

In another letter Sir John said the committee would be "disappointed" if Mr Blair was "less forthcoming in his evidence" during his appearance before the panel on Friday, which follows another public hearing last year.

Sir Gus is himself scheduled to give evidence on 28 January.

A Downing Street spokesman said the decision to prevent publication of the Blair-Bush exchanges had been "very clearly a cabinet secretary decision", as set out in the inquiry's protocol.

"The PM had no role in that decision," he added, saying there were no plans to change this way of working.

Sir John's five-member panel questioned Air Chief Marshal Sir Glenn Torpy, former chief of the air staff, on Tuesday.

He was asked about his role as the UK's air component commander for the March 2003 invasion of Iraq.

'Uncomfortable'

Sir Glenn was also the military's chief of joint operations from 2004 to 2006 before leading the RAF from 2006 until 2009.

The inquiry is looking into the UK's role in the run-up to the invasion and its aftermath.

It has been holding hearings since November 2009, in which it has questioned a host of former Labour cabinet ministers, senior military commanders, civil servants and diplomats. The inquiry is expected to report in the summer.

Written evidence from former attorney general Lord Goldsmith, released on Monday, showed he had been uncomfortable about statements by Mr Blair before the 2003 invasion.

In addition to Mr Blair, the inquiry has also recalled former Foreign Secretary Jack Straw, Admiral Lord Boyce, chief of the defence staff from 2001 to 2003, and Lord Turnbull, cabinet secretary from 2002 to 2005.

In a written statement, which was made public by the Iraq inquiry on Monday, Lord Goldsmith said Mr Blair's public suggestion in January 2003 that Britain could attack Iraq without further UN backing had not been compatible with his legal advice.

He said he could not remember precisely when he had become aware of the comments, but told the inquiry: "I was uncomfortable about them and I believe that I discussed my concerns with [then foreign secretary] Jack Straw and my own staff..."

He also told the inquiry he understood the need to make public statements which "left Saddam Hussein in no doubt about our firmness of purpose".