Kevin Rudd has spoken publicly against the Prime Minister's handling of his bid for the United Nations' top job, describing Malcolm Turnbull as a "brick wall".

Key points: Rudd says decision part of 'scar-tissue' of life

Rudd says decision part of 'scar-tissue' of life Turnbull criticises Rudd for releasing private correspondence

Turnbull criticises Rudd for releasing private correspondence Shorten says Turnbull has explaining to do over decision-making process

The former prime minister addressed a Young Labor function in Brisbane on Saturday, a day after being told the Federal Government would not endorse his bid to become the next secretary-general.

He said it was part of the "collective scar-tissue" of life.

"Sometimes, it will turn to shit," he said.

"And sometimes it won't work out perfectly. I've had modest experience with that. Just a little bit around the edges, including yesterday."

Mr Rudd's comments follow the release of his private correspondence to Mr Turnbull, something for which the Prime Minister has criticised Mr Rudd.

In the three letters, dated earlier this year, Mr Rudd wrote Mr Turnbull had previously told him he would support his bid.

Addressing media yesterday, Mr Turnbull said the letters' account of what happened was "absolutely untrue".

"They were all confidential discussions, they were all private conversations," he said.

"It says a lot about Mr Rudd that quite some time after the event he would seek to present an account of them in correspondence, he would write to me with the clear intention of subsequently releasing it."

But Opposition Leader Bill Shorten said Mr Turnbull had "a fair bit of explaining to do".

Mr Shorten told the ABC on Tuesday "poor old Foreign Minister Julie Bishop" tried to do the right thing, but Mr Turnbull was pressured by his conservative colleagues.

"It's clear to me that Mr Turnbull's put his own political survival ahead of prior positions he may have had," he said.

"The right-wing puppet masters of Mr Turnbull's Government pulled the strings and he's danced to the string-pulling."