Labour has all but ruled out forming a coalition with the SNP, in a dramatic move which suggests Britain could be heading for a minority government.
Asked whether he would consider a coalition with Nicola Sturgeon's party, shadow chancellor Ed Balls replied: "No".
"I don't think anybody is suggesting a deal with the SNP at all. We're fighting hard for a majority," he told Sky News.
Asked whether he thinks a minority government would be more likely, he told LBC that the public would be unlikely to accept another coalition.
"Back in 2010... the idea of a coalition was popular and the idea of Nick Clegg and the Lib Dems was popular. Five years on, the idea of a coalition is very unpopular and the idea of Nick Clegg is even more unpopular," he added.
Current opinion polls suggest that neither the Conservatives nor Labour are likely to be able to form an outright majority, with some polls suggesting a coalition of at least three parties would be necessary.
Given the difficulties this would pose, both main parties are increasingly considering the possibility of governing alone instead, in advance of a possible second election.
Balls' comments were also designed to close off a recent attack from the Conservatives.
Last week, the Tories unveiled an election poster depicting Ed Miliband arm in arm with Alex Salmond outside Downing Street with the slogan "Your worst nightmare… just got worse".
However, while a formal coalition between the two parties now looks unlikely, Balls' comments do not rule out a less formal deal between the two parties, including a so-called 'confidence and supply' arrangement.
Such an arrangement would be more likely to suit the SNP, given the damage a more formal deal could do to their own future electoral chances.
Balls' comments will come as a blow to the Liberal Democrats who are pitching themselves to voters as best placed to 'moderate' the major parties in a future coalition.
This morning they released a new poster, suggesting that both the Tories and Labour would make Britain "veer off course" if they are allowed to govern alone.
Britain needs a liberal voice in govt to stop Labour and the Conservatives from lurching to the left and right pic.twitter.com/4kSVGrGubn— Liberal Democrats (@LibDems) January 27, 2015
The poster was a deliberate parody of another recent poster released by the Tories urging voters to "stay on the road to a stronger economy".
The Lib Dems' approach has been criticised by some senior figures in the party who accuse them of trying to "split the difference" between the two parties.
They warn that this approach is doomed to fail given the party's collapse in support since entering coalition.