Turnbull rejects Rudd for UN job

Australia won't be nominating former prime minister Kevin Rudd for the top job in the United Nations.

A split in federal cabinet on Thursday meant Prime Minister Malcolm Turnbull was left to make a captain's call on whether to nominate Mr Rudd for secretary-general of the United Nations.

"I have spoken to Mr Rudd in the last hour and advised him of that decision and the reasons for it," Mr Turnbull told reporters in Sydney on Friday.

Mr Turnbull told reporters he would not go into the cabinet discussion.

"I do not want to add to Mr Rudd's disappointment, but the threshold point here is when the Australian government nominates a person for a job, particularly an international job like this, the threshold question is: do we believe the person, would-be nominee is well suited for that position?

"My judgment is that Mr Rudd is not, and I've explained to him the reasons why."

Mr Turnbull denied he was playing politics, insisting the decision had nothing to do with the Labor party.

The government had supported former Labor politicians for important positions in the past, including extending former Labor leader Kim Beazley's term as ambassador to Washington.

"This is no disparagement of Mr Rudd," he said.

"He is a former prime minister of Australia but my judgment is that he is not well suited for this particular role."

Asked why he went against his deputy leader Julie Bishop on the decision, Mr Turnbull said he would not detail discussions of cabinet.

The prime minister also refused to say whether he would back New Zealand candidate Helen Clark, saying the government would consider others in due course.