Australian Prime Minister Malcolm Turnbull is not obligated to back a potential bid by Helen Clark for the top United Nations job, despite a commitment by his predecessor, Prime Minister John Key says.

Mr Key spoke to his Australian counterpart on the weekend after it was revealed that former Prime Minister Tony Abbott agreed to support Ms Clark in the event that she became a candidate for the Secretary-General of the United Nations.

Mr Turnbull's cabinet was now planning to overturn this commitment, the Australian newspaper reported.

Mr Key today confirmed that he sought Mr Abbott's support when it became apparent that Ms Clark might run as a candidate."[Mr Abbott] said at the time 'Look if she puts her name forward I would have thought Australia would support that'," he said.

Advertisement
Advertise with NZME.

The two leaders formalised the agreement in a letter.

Mr Key said the situation had changed now that Mr Abbott was no longer in charge.

"Once the change of prime ministership happened, we wouldn't it consider it a binding obligation," he said.

The Australian Government's change of position was down to two factors, according to the Australian.

Mr Abbott did not consult his Foreign Minister Julie Bishop about the agreement. And former Prime Minister Kevin Rudd had expressed an interest in the UN position.

Mr Key said he was unaware that Ms Bishop had not been informed of the commitment.

He still hoped that Australia would back Ms Clark if she ran as a candidate.

"She's got all the credentials, she's extremely capable and personally [and] frankly I hope she puts her name forward and gets the job.

"I'm more than happy to continue to make the case as I would to any other leader I could talk to if she put her name forward."

However, he did not expect Australia to back Ms Clark over Mr Rudd if both were competing for the role.

Mr Key did not know whether New Zealand would support Mr Rudd if Ms Clark was not in the contest, saying it would have to be discussed with Foreign Affairs Minister Murray McCully.

UN Secretary-General Ban Ki-Moon's term finishes this year.