A leading Labour MP has said a potential coalition deal between his party and the Lib Dems would not include the Scottish National Party.
Douglas Alexander said he could not envisage circumstances in which Labour would enter an agreement with the SNP.
Mr Alexander, one of Gordon Brown's closest allies, said the parties had "fundamental" differences.
SNP leader Alex Salmond said Mr Alexander should "get off his high horse" and be "more conciliatory".
The SNP has made calls for a rainbow alliance of all the "progressive" parties at Westminster.
This would involve the SNP, the Welsh Nationalists, some MPs from Northern Ireland and the sole Green MP, as well as Labour and the Lib Dems.
Mr Salmond, Scotland's first minister, said: "We have never wanted to be part of a coalition with any of the London parties.
"If the Labour Party want to stay in government they should get off their high horse and see the world from other people's point of view."
Mr Salmond said there were two options to be considered.
He said: "Either we can look at things on a vote by vote basis and do what is in the interests of the Scottish people or there could be a longer-term arrangement.
"Again it would have to be based on what is in the interests of the Scottish people."
The Conservatives got the most seats at Thursday's general election but not enough for an overall majority at Westminster.
Labour's Tom Harris and Neil Kinnock divided over PR
The Tories have been negotiating with the Lib Dems over a coalition deal.
The Lib Dems have also been talking to Labour about the possibility of forming a government.
Lib Dem MP Simon Hughes echoed the comments of Mr Alexander by saying a two party coalition with Labour would be possible.
He said the Nationalists in Scotland and Wales may be called on to support "crucial" votes.
Mr Alexander, the MP for Paisley and Renfrewshire South MP, said it was right for Labour to engage in formal negotiations with the Lib Dems to see if common ground could be established.
He said no party had a working majority.
"It is perfectly reasonable, indeed it is constitutional, that these discussions are now taking place because we need to get to a position where somebody is able to command a majority in the House of Commons," he said.
Mr Alexander added: "I can assure you I have had no contact with the SNP, nor has the chancellor, the Scottish secretary or the prime minister because there are fundamental differences between the Labour Party and the Scottish National Party.
"Personally, I can't envisage circumstances in which we would enter into agreement with the Scottish National Party."
Fellow Scottish Labour MP Tom Harris said his party should not be trying to get a coalition deal with the Lib Dems.
The MP for Glasgow South told BBC Radio Scotland such a deal would not bring a stable government.
Mr Harris said: "We are in this position because we lost the election.
"I am worried about the long-term future of the Labour Party if we are seen to scrabbling around in a very ungracious way desperately trying to hold on to power in any and all circumstances."
Mr Harris added: "It seems to me we are not talking about a rainbow coalition. We are talking about Labour plus the Liberal Democrats, supported whenever the Nationalists feel like it on crucial issues.
"That does not equate at all to a stable long-term government arrangement."
There's probably about a third of the party that opposes working with the Conservatives, about a third of the party that opposes working with Labour and the final third doesn't want to work with either of them
Nicol Stephen Scottish Liberal Democrat leader
Former Tory Foreign Secretary Malcolm Rifkind said Labour attempts to form "a coalition of the defeated" was a "negation of democracy".
He said a government "cobbled together" between Labour and the Lib Dems would be "illegitimate".
Mr Rifkind, the MP for Kensington, said the Tories got two million more votes than Labour.
He said: "The idea that the two parties that suffered most in this election, that were rejected by the electorate, should put together an illegitimate government - this is Robert Mugabe-style politics.
"That's exactly what Mugabe did. He lost the election and scrabbled to hang on to power in the most illegitimate way."
Meanwhile, former Scottish Liberal Democrat leader Nicol Stephen conceded a deal with the Tories would be "difficult" for Lib Dems in parts of the UK.
Mr Stephen told BBC Radio's Good Morning Scotland programme: "Many of us got into politics during the Conservative years in government, the Thatcher years, and we have deep-seated concerns about Conservative policies."
He added: "It's difficult for us. There's probably about a third of the party that opposes working with the Conservatives, about a third of the party that opposes working with Labour and the final third doesn't want to work with either of them."
Of the talks with Labour he said: "If we know what the Labour Party is offering, that will allow us to fast-track the alternatives if negotiations with the Conservatives are not successful.
"It surely would be quite wrong to go back to square one if the negotiations with the Conservatives broke down."
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