Australia's foreign minister has resigned amid an ongoing leadership squabble, saying he cannot continue in his role without the support of prime minister Julia Gillard.

Foreign minister Kevin Rudd announced his resignation during an early morning news conference today in Washington, where he is visiting on official business.

His decision comes amid relentless speculation that he planned to seize power from Ms Gillard.

Ms Gillard came to power in an internal coup within her Labour Party that ousted Mr Rudd as prime minister in June 2010.

She became only the third prime minister since the Second World War to gain power in this way.

"I can only serve as foreign minister if I have the confidence of prime minister Gillard and her senior ministers," Mr Rudd said.

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

In recent days, speculation had been mounting that Mr Rudd's supporters were planning an attempt to restore him to power soon. That had become a distraction, Mr Rudd said.

"The truth is the Australian people regard this whole affair as little better than a soap opera and they are right," he said. "And under current circumstances, I won't be part of it."

It was not immediately clear what Mr Rudd's next move would be. He said he planned to fly back to Australia tomorrow to sort out his future.

But in his resignation speech, he was highly critical of the Labour Party's decision to oust him.

"I can promise you this: There is no way - no way - that I will ever be party to a stealth attack on a sitting prime minister elected by the people," Mr Rudd said.

"We all know that what happened then was wrong and it must never happen again."