‘‘There is no way I will ever be party to a stealth attack on a sitting prime minister who was elected by the people.’’

He said the Prime Minister's failure to repudiate Simon Crean and other cabinet ministers' attacks on him throughout the week had been central to his decision to resign as Foreign Minister.

Mr Rudd took aim at Ms Gillard’s poor standing in the polls.

Mr Rudd said there had been some "similar factors at play" in June 2010 when he lost the prime ministership.

"It's time for some plain speaking on this," he said.

"The truth is I can only serve as foreign minister if I have the confidence of Prime Minister Gillard and her senior ministers.

"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.

"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."

"There is one overriding question for my colleagues and that is who is best placed to defeat Tony Abbott," he said.

"Tony Abbott is on track to win and has been for a long time."

Mr Rudd said he was sad to leave the office.

"The simple truth is I cannot continue to serve as foreign minister if I do not have Prime Minister Gillard's support," he said.

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

Australia must be governed by the people, not party factions, Mr Rudd said.

"I promise you this - there is no way, no way, that I will ever be part of a stealth attack on a sitting prime minister elected by the people," he said.

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

Mr Rudd said he had few options in announcing his resignation overseas.

"The truth is I feel very uncomfortable doing this from Washington and not in Australia," Mr Rudd said.

"But I don't feel like I have a choice given the responsibilities over the days ahead."

Mr Rudd said the ongoing leadership speculation about the federal party was hurting Labor's prospects in the coming Queensland election.

He said the saga was bad for his friend, Queensland premier Anna Bligh.

"I believe the good people of Queensland deserve some clear space over the coming month as they make up their minds on a very important decision on the future of Queensland, my home state," he said.

Mr Rudd's daughter Jessica tweeted: "Effing proud of you, Dad xxxx".

His wife Therese Rein responded: "Me too, Kevin xxxx".

Mr Rudd said he would fly out of Washington tomorrow morning and he is due to arrive home in Brisbane on Friday morning.

"Under no circumstances do I want Australia’s international reputation brought into disrepute because of this ongoing saga,’’ he said.

‘‘Therefore, Ambassador (Kim) Beazley will discharge my functions here on my behalf in Washington tomorrow and the permanent secretary of my department, Dennis Richardson, will represent me in London and in Tunis.’’

He ended the extraordinary press conference without taking questions, saying there was "much, much to do".

Meantime, veteran Labor strategist - and close personal friend of Mr Rudd's - Bruce Hawker said he believed the former foreign minister would challenge for the leadership, citing his consistent popularity in the polls and in the electorate.

Mr Hawker said that backbench MPs would consider their self-interest in retaining their seats at the next election when deciding on the Labor leadership.