Kevin Rudd is set to contest the Labor leadership, he has told reporters in Washington DC.
''I do not believe that Prime Minister Gillard can lead the Australian Labor Party to success at the next election,'' he said.
Mr Rudd, who will give a fuller statement on his return to Australia, said he was encouraged by support from colleagues overnight but "shocked" by personal attacks against him since he resigned.
''I would urge my own supporters in Australia, not to retalitate,'' he said.
He added that Mr Abbott was the ''national master'' of this type of politics.
He has called on Australians to cultivate a new culture of unity in response.
''In Australia today, people are stick and tired of the politics of division,'' Mr Rudd said.
Mr Rudd said that politics in Australia was not about personality, but about trust and vision.
''We have done some formidable things,'' he said, citing new investment in hospitals, education and the NBN, as well as dealing with challenges of climate change and the indigenous apology.
Mr Rudd said that a key future challenge was the restoration of business confidence.
''That is critical'', he said, adding that small business needed to be encouraged to invest in their future.
He added that the second big challenge was manufacturing.
''I do not share the view that manufacturing is somehow old-fashioned,'' he said and he slammed the Gillard government's decision to axe the Green Car Fund.
The third big area of policy, Mr Rudd continued, was health reform, saying the government has ''squibbed'' some of the big decisions when it came to health.
He also said he wanted to tackle further reform of the education system, saying he wanted to have an emphasis on Asian languages.
Also on the list was reform of the Labor Party itself, Mr Rudd said, so that it was not governed by ''faceless men''.
This is the second press conference that Mr Rudd has held in under 24 hours. He said that he wanted to call this second meeting, as he will soon be on a plane travelling back to Australia and out of contact.
Earlier his strong supporter, Labor Senator Doug Cameron, called on Julia Gillard to delay the Labor leadership ballot until next Friday, as the Prime Minister prepares to announce a vote for Monday morning.
Ms Gillard will hold a press conference from her hometown in Adelaide at 9am (9.30am AEST) - having chosen not return to The Lodge to reply to Kevin Rudd's shock resignation from his foreign affairs post.
Last night, prominent Rudd backer, Senator Cameron said that a ''rush to a ballot'' on Monday would not be a ''fair go'' for Mr Rudd.
''I think that would be a travesty of democracy within the Labor party,'' Senator Cameron told the ABC's Lateline.
Senator Cameron - of the Labor left faction - said that Mr Rudd needed time to return from overseas and campaign. Today, The Sydney Morning Herald reports that Mr Rudd is short of a majority with between 30 and 39 votes - depending on the views of the Gillard or Rudd camps. He would need 52 votes to take the leadership.
Treasurer Wayne Swan this morning announced that he has cancelled his trip to the G20 Finance Minister's meeting in Mexico this weekend in anticipation of a Monday vote on the Labor leadership.
''This morning I contacted the meeting's host, the Mexican Finance Minister, Mr Jose Antonio Meade, to advise him of this and my disappointment in not attending,'' Mr Swan said in a statement.
Finance deputy Mike Callaghan will represent Mr Swan.
Meanwhile, reinstalling Mr Rudd as prime minister could affect the support of key independent MPs, which the government needs to hold office, with crossbencher Tony Windsor hinting this morning that it is unlikely he would back a Rudd prime ministership mid-term.
The NSW independent told the ABC that he was ''more than happy to talk to anybody'' in the event that there was a leadership change.
But he added it would be ''difficult'' to come to ''another arrangement'' in the middle of a parliament.
Mr Windsor said that he thought he had a much chance of becoming Prime Minister as Kevin Rudd did. ''I don't think there will be a new leader,'' he said.
Mr Rudd is currently camped in The Willard hotel in Washington DC, where it is mid-afternoon local time, and has not been seen by reporters today.
He was due to give a speech at the Carnegie Endowment for International Peace on Wednesday morning. The organisation's website site now carries a picture of a serious looking Mr Rudd and an apology.
''Please accept our apologies. In light of Kevin Rudd's resignation as foreign minister earlier this morning, today's event is cancelled.''
Australia's Ambassador to the US and former Labor leader, Kim Beazley has visited Mr Rudd at his hotel. Mr Beazley brushed off questions about Mr Rudd, noting that the leadership battle will be decided by people "well and truly above my pay grade".
This morning Attorney-General Nicola Roxon said a leadership ballot was inevitable.
''We have to put this issue to bed,'' she told the ABC. ''We have got to be mature.''
Ms Roxon noted that Mr Rudd had led the ALP to victory in 2007 and had achieved ''some amazing things.''
But she added that he was very difficult to work with as prime minister.
''That decision [to dump him] was made for very strongly held reasons that I think are still true now.''
Other senior ministers have come out to criticise Mr Rudd since he resigned.
Communications Minister Stephen Conroy called Mr Rudd’s destabilising behaviour behind-the-scenes a ''disgrace'' early this morning on Channel 9.
Trade Minister Craig Emerson – who will act as Foreign Minister – said that Mr Rudd’s statement that he would not attack a sitting prime minister was hypocritical.
''I think Kevin should look in his own backyard''.
Last night, Environment Minister Tony Burke added that he was glad the leadership issue was being resolved.
''The fact that Kevin's been openly campaigning for the leadership has been the worst kept secret in Canberra,'' he told 7.30.
But Labor backbencher Janelle Saffin said the spate of senior Gillard ministers ''entering the fray and criticising Mr Rudd was ''unseemly''.
Ms Saffin also told ABC radio this morning that that people in her northern NSW electorate wanted to see Mr Rudd return as prime minister. She said Australians had elected him in 2007 and saw his dumping as ''wrong'' and Labor had been ''paying the price ever since''.