Speculation that Australian support for any Helen Clark bid for the top United Nations job could be overturned comes amidst jostling by potential candidates, Labour's foreign affairs spokesman David Shearer says.

Malcolm Turnbull's Australian cabinet may overturn a commitment given by former Prime Minister Tony Abbott to back Helen Clark for Secretary General of the United Nations if she becomes a candidate, according to The Australian newspaper.

The paper revealed that Mr Abbott and Prime Minister John Key committed in letters to conduct a joint strategy to promote Ms Clark as the successor to Ban Ki-Moon whose term ends at the end of this year.

But that commitment looks set to be compromised by two factors: Mr Abbott did not consult his Foreign Minister, Julie Bishop, before giving the undertaking to Mr Key.


And former Australian Prime Minister Kevin Rudd has made it known he is interested in the job.

Mr Shearer said that he would have expected Australia to be a strong supporter of Ms Clark if she was confirmed as a candidate, but it was very early in the process.

"It is early days and at this stage, from what I am picking up, there is a lot of jostling and looking and talking to people about where support lies."

Mr Shearer said there were a number of possibilities, and Australia could swing behind Ms Clark if Mr Rudd pulled out or decided not to run after taking soundings.

Ms Clark has not publicly expressed her interest in the job but it is an open secret she would like it and Mr Key would not have been seeking Australia's help without her consent and private ambition for the post.

Mr Key has publicly expressed strong backing for her, should she put up her hand.

According to The Australian, the letter Abbott wrote to Mr Key said Ms Clark would prove "a strong voice at the top of the United Nations" and that she had "the leadership, management skills and purpose to drive the United Nations forward for the benefit of the entire international community."

If Mr Rudd sought the post, Australia would be obliged to support him.

Helen Clark is already number three in the United Nations hierarchy as head of the United Nations Development Programme.

Her potential candidacy could be helped by a lobbying to get a woman to the head the body after eight males.

The general assembly last year decided to formally call for nominations and encouraged countries to nominate women.

But Eastern Europe and Russia sees it as its "turn".

The rules say that the general assembly makes the appointment on the recommendation of the Security Council - on which five countries have veto rights.