Former Australian Prime Minister Kevin Rudd has asked the Australian Government to formally nominate him for the Secretary General's role at the United Nations, which will pit him against Helen Clark.

Australia's Foreign Minister Julie Bishop told Australian media Rudd had put in a request for nomination just four days before the Security Council holds its first straw poll on a shortlist. There are 12 candidates so far.

Bishop told Sky News she would put his request to Cabinet to decide on.

"Kevin Rudd has requested that the Australian government nominate him and as [Malcolm Turnbull] has indicated on a number of occasions that will be a matter for the cabinet."

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There has long been speculation Rudd was aiming for the post although Rudd had refused to confirm it.

In April he was dismissive of Clark's chances of success saying she was "very capable" but it was his "firm belief" that an Eastern European would get the job. He said the only chance would be if the five Permanent Members on the Security Council could not agree on an Eastern European candidate. "Last time I looked my name was not Ruddovich."

Australia had held off endorsing Clark's bid while it waited for Rudd to make a decision. Prime Minister John Key has previously said he would expect Australia to support Rudd if he did go for it because he was Australian. However there have been mixed views about Rudd in the Australian Government. Immigration Minister Peter Dutton has also scoffed at Rudd's ambitions in the past: ""Kevin was never happy just running Australia - he believed he was always destined to run the world," he said. "Kevin's ego makes Donald Trump's look like a rounding error."

South Australian Liberal senator Cory Bernardi previously urged Bishop against supporting Rudd, describing him as "vengeful" "unstable" and a "megalomaniac."

An Essential poll in Australia in April showed Australians backed Clark over Rudd - 45 per cent of the 1020 polled said Clark would be a better leader for the UN compared to 21 per cent for Rudd.

Although it will be the Security Council which decides on a final candidate for the General Assembly , this year the General Assembly has tried to make it a more open process than in the past. That has included requiring candidates to address the General Assembly and take questions. Most also took part in a debate hosted by Al Jazeera last week.

In a short post on Facebook, Rudd wrote he respected the internal processes of the Australian Government.

"I respect the fact that the Government has many other priorities at this time, having just been returned to office.

This is a matter for the Prime Minister, the Foreign Minister and their colleagues at a time of their choosing."

He did not make any further comment.