The "frenzied" social media attacks from supporters of Labour leadership contenders on rival candidates must end for the good of the party, Yvette Cooper has said.
The shadow home secretary said all sides should act in a "comradely" way in response to heated online debates, fuelled by supporters of the left-winger Jeremy Corbyn.
Ms Cooper said that there had been "too much polarising" in the leadership contest and whoever won would have to pull the party back together again.
She has predicted the party could split if Mr Corbyn, who has emerged as the shock frontrunner to take control of Labour on September 12, won. But she acknowledged that even if she, Andy Burnham or Liz Kendall emerged as the winner they would have to reunite the party.
She told the Press Association: "That's what I believe we need to do, in the same way that you pull the family back together again, we have got to unite our party.
"I think there has been too much polarising in this debate between people saying 'you have got to choose between your head and your heart', 'you have got to choose between principles and power'.
"I don't think that is right. We have to do both. We have to have the radical ideas about the future, we also have to be credible enough to turn them into practice. That is what we have always done as part of Labour's history - we have said let's have the vision for the future and then let's make it happen.
"There are a lot of ideas about human rights, about tackling homelessness, all those sorts of things, where Jeremy and I strongly agree. But I think we have different ideas about what are the answers to put it into practice.
"But I think you can unite around the ideas and vision for the future and pull the party together again."
She admitted she was concerned about the bitter nature of the online debate, which has seen supporters of rival candidates subjected to attacks on Twitter. People who speak out against the hard-left Mr Corbyn are routinely labelled as "Tories" by his supporters.
Ms Cooper said: "I think the problem with the social media debate is that it can become quite frenzied, from all sides. I don't think that's helpful.
"It's why I don't think this should be about personalities or about personal attacks in any way. This should be about policies and ideas.
"We are a political party - we should be able to debate policies and ideas and answers in a way that is actually very comradely, that is about respect for each other's ideas but have honest disagreement. That's probably easier to do in a room, and in a debate and a conversation than it is in 140 characters. But actually it would be a good thing if everybody on social media had those principles at heart as well."
Sources in Ms Cooper's camp have played down reports that Gordon Brown is set to endorse her for the leadership, but the shadow home secretary has said she has spoken to the former prime minister. Mr Brown is due to address the future of the party in a speech on Sunday.
"I have spoken to Gordon, I have spoken to lots of different people as part of the campaign, just asking people about their ideas for the future and so on," she said.
One endorsement which Ms Cooper probably did not expect - or possibly want - came from the ConservativeHome website which said that Labour should elect a female leader, saying the Tory party "didn't do badly when it chose a woman".
Ms Cooper, who represents Normanton, Castleford and Pontefract in Parliament, said: "As a coalfield MP, I'm not sure I think there's a great comparison with Margaret Thatcher. I also think she didn't do a huge amount to help women either."
But she added: "I think it would be fantastic if we could smash that final glass ceiling in the Labour Party and shake up the Westminster old boys' network and have our first elected woman leader and, more importantly, an elected Labour woman prime minister that can actually change Britain."