Australian Foreign Minister Kevin Rudd has resigned, saying he could not continue without Prime Minister Julia Gillard's support amid speculation he will challenge her for the leadership.

"The simple truth is that I cannot continue to serve as foreign minister if I don't have Prime Minister Gillard's support," he said in a late night press conference in Washington broadcast live in Australia.

"I therefore believe the only honourable course of action is for me to resign."

Australia's Labor government has been torn by speculation about whether Mr Rudd, who Ms Gillard suddenly ousted as a prime minister in mid-2010 but who remains hugely popular, would mount an attempt to return to the top job.

Mr Rudd said he would head back to Australia this week and make a full statement on his future before parliament resumes on Monday.

"In recent days Mr (Simon) Crean and a number of other faceless men have publicly attacked my integrity and therefore my fitness to serve as a minister in the government," he said, referring to the former Labor leader.

"When challenged today on these attacks Prime Minister Gillard chose not to repudiate them. I can only reluctantly conclude that she therefore shares these views."

Reports earlier today said Ms Gillard was so confident she has the support of Labor MPs she will call a leadership ballot on Tuesday.

They said that if Mr Rudd loses, he would immediately be sacked as foreign minister by Ms Gillard and moved to the backbench.

Australia's next national election is due in 2013.