Australia refused on Friday to back former prime minister Kevin Rudd's bid to be the next secretary general of the United Nations, saying he was not suited to the job.

Rudd was spectacularly dumped as prime minister by his own Labor Party in 2010, with colleagues subsequently alleging that his office was chaotic and he was difficult to work with.

"This is not a partisan issue, this is a considered judgment," Prime Minister Malcolm Turnbull, who is from the rival Liberal Party, said when announcing the decision in Sydney.