Media playback is unsupported on your device Media caption Kevin Rudd was sworn in, promising to do his ''absolute best''

Kevin Rudd has been sworn in as prime minister of Australia, a day after he ousted Julia Gillard as leader of the Labor Party.

Mr Rudd took the oath at Government House in front of Governor-General Quentin Bryce.

He then addressed parliament briefly, paying tribute to Ms Gillard, who is stepping down from politics.

The leadership change comes ahead of an election scheduled for 14 September, which polls suggest Labor will lose.

Opposition leader Tony Abbott called on Mr Rudd to clarify whether the election would be brought forward.

"I congratulate the prime minister on his restoration to high office," he said. "May he elevate that office... by telling the Australian people when will they get the chance to decide who the prime minister of this country should be and who should form the government of this country?"

Media reaction By calling on a ballot and demanding the loser leave politics, Gillard has ensured her role in the ousting of Rudd almost three years ago and the ensuing national schism will in time pale alongside her achievements... A competitive contest is good for Australia. Thanks to Julia Gillard's decision, we now have one. (Editorial, Sydney Morning Herald) [Mr Rudd's] task now is to resume office without the hubris that consumed his first term as prime minister... Neither will Mr Rudd get far by presenting himself simply as the candidate who is not Mr Abbott. He must recognise that Mr Abbott is now an opposition leader of experience and stature who, like Mr Rudd himself, has been strengthened by the experience of the past three years. (Editorial, The Australian) Julia Gillard has delivered the ultimate act of leadership and paid the ultimate price, ending the most poisonous, inglorious chapter in modern Labor Party history. But whether Kevin Rudd transforms Labor's prospects at the election depends on whether he can re-unite a fractured party that he helped divide, re-connect with a hostile electorate and challenge a rampant opposition. (Michael Gordon, political editor, The Age) The more Labor squabbles, the more it turns on itself, the more the Liberal and National parties are spared the necessity of presenting a coherent platform for election. Why, in the circumstances, should they bother?... Never mind its three-year obsession with leadership, with that at last behind it the [Labor Party] really ought to have a stab at leading, even if it is to defeat. (Jonathan Green, ABC's The Drum blog) Rudd: Saviour or 'recycled failure'? Magazine Monitor: Disemvowelled

Mr Rudd said he would "identify a date for an election", suggesting that he would not stick with the date set by Ms Gillard.

"There's going to be an election, it will be held consistent with the constitution and... there's not going to be a huge variation one way or the other," he said.

'Energy and purpose'

Mr Rudd returned to lead Australia's government three years and three days after he was toppled in a similar Labor leadership contest by Ms Gillard, then his deputy.

He secured 57 votes to Ms Gillard's 45 in Wednesday's vote, which followed months of speculation and bitter infighting over who should lead Labor into the forthcoming election.

Opinion polls have suggested Labor will suffer a crushing defeat. But Mr Rudd is more popular with voters than Ms Gillard and many believe the party will perform better under him.

Speaking after his win on Wednesday, Mr Rudd said he resumed the role of prime minister with "an important sense of energy and purpose".

"Why am I taking on this challenge? For me it's pretty basic, it's pretty clear. I simply do not have it in my nature to stand idly by and to allow an Abbott government to come to power in this country by default," he said.

Ms Gillard resigned as prime minister on Wednesday and said she would leave politics, as she and Mr Rudd had agreed the loser would before the vote.

Despite their bitter rivalry, Mr Rudd praised his predecessor when he addressed parliament shortly after being sworn in.

"Through the difficult years of minority government the former prime minister has achieved major reforms for our nation that will shape our country's future," he said.

"On top of all that, I acknowledge her great work as a standard bearer for women in our country."

Describing politics as a "very hard life", he also called on fellow lawmakers "to be a little kinder and gentler with each other".

He added that further information on his ministerial line-up would come later.

Anthony Albanese has been sworn in as deputy prime minister and Chris Bowen replaces Wayne Swan as treasurer.

Six of Ms Gillard's ministers resigned after the party vote and further shake-ups are expected.

Ms Gillard's government depended on the support of independents for its majority - reports suggest that enough of them have swung behind Mr Rudd to give him control of parliament.

The BBC's Nick Bryant, in Sydney, says it is an astonishing return for a politician who has long been popular with the public at large but despised by senior colleagues within his party.

It is a measure of his unpopularity that a third of Julia Gillard's ministry resigned rather than serve under him, our correspondent adds.