Will Kevin Rudd challenge Australian PM?

Mr Rudd could be about to take the biggest gamble of his career

Australia's gripping political soap opera has taken another unexpected twist with the resignation of Foreign Minister Kevin Rudd.

His surprising decision to quit on a trip to North America almost certainly means he will mount a challenge to Prime Minister Julia Gillard, possibly as early as next Monday, when parliament resumes.

Tensions between the pair have quietly festered since Ms Gillard toppled Mr Rudd in June 2010 during his first term as prime minister. In recent days, the rivalry has intensified and is set to become an all-out brawl.

Gillard loyalists had accused the former foreign minister of betraying the government as he sought to mobilise support for a sensational comeback.

"In recent days… a number of… faceless men have publicly attacked my integrity and therefore my fitness to serve as a minister in the government," Mr Rudd told a late-night press conference in Washington.

"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."

Party support

Crucially, the ex-diplomat from Queensland did not rule out a tilt at the leadership. He is expected to arrive home in Brisbane on Friday to consult his family and his political allies, and begin to crunch the numbers.

Mr Rudd's supporters insist that he already has the backing of 40 members of the federal Labor caucus in Canberra and was confident of picking up a further 12 votes needed for victory.

Ms Gillard's advisers have laughed off such lofty claims and believe the Welsh-born prime minister would cruise to a crushing win in any leadership ballot.

Mr Rudd is a naturally cautious operator, but could be about to take the biggest gamble of his career. Wavering MPs will either appreciate his boldness and consider him their best chance of success at the next election due in 2013 or punish him for disloyalty.

Opinion polls have repeatedly indicated that the Gillard government would lose heavily if an election was held today.

Dr Norman Abjorensen, a lecturer in political science at the Australian National University, says Mr Rudd's tactics so far "could either crash through and achieve a breakthrough for him or… create quite a very strong backlash. An approach like this could well kill his chances altogether."

For now, the man known in sections of the media as "a happy little Vegemite" heads back to the backbench.

Writing in the Sydney Morning Herald, senior correspondent Daniel Flitton said Australia's minority government was being ripped apart.

"One exasperated Labor MP told me this morning to see Labor's leadership battle was akin to watching an ugly, messy divorce. Everything built over the years by Kevin Rudd and Julia Gillard since 2006 is being torn apart. What is hardest in any divorce is it forces the family to chose sides," he said.

'Dog's breakfast'

Ms Gillard's advisers believe she would cruise to a crushing win in any leadership ballot

The uncivil war within the governing party could have mixed results for the opposition, which has described the infighting as "a dog's breakfast".

A victory for Kevin Rudd would most likely unsettle conservative forces, which have rained down unrelenting and ferocious blows on Ms Gillard since the last election in August 2010.

They smell blood, but a return of Prime Minister Kevin Rudd, arguably one of Australia's most popular politicians, could dim their chances of electoral success.

In typically combative style, the opposition leader Tony Abbott said the Labor party had become a national embarrassment.

"Kevin Rudd's statement tonight confirms that this government is unworthy to continue in office," said Mr Abbott.

The former foreign minister is heading home to a very uncertain future, although he can rely on the support of his family. Following his resignation, his daughter Jessica and wife Therese Rein immediately tweeted that they were proud of him.

Mr Rudd will be hoping enough of his Labor colleagues also feel the same way should he challenge the woman who ousted him almost two years ago.