SCOTS Lib Dem leader Willie Rennie has said he would be willing to work with the SNP after next year's Holyrood election if no party emerges with a majority.
In an interview with The Herald, the MSP said a deal would only be possible if the Nationalists ruled out a second independence referendum.
His comments were seized on by Scots Tory leader Ruth Davidson, who ruled out any deal with the Nationalists at Holyrood.
Mr Rennie echoed UK party leader Nick Clegg when he rejected the possibility of the Lib Dems joining any Westminster alliance which included the SNP.
He said: "It's not really reasonable to put a party that is against the United Kingdom in charge of the United Kingdom."
But, referring to Holyrood, he added: "It's not that we are against working with the SNP at other levels.
"We could work with them.
"We'd have to have to pretty clear about ruling out a referendum but other issues we could have discussions on."
Mr Rennie, who repeated his comments on the BBC's Sunday Politics, also opened the door to a possible deal with Labour after the 2016 poll.
Ms Davidson said: "It is astonishing that the Scottish Lib Dems are willing to prop up and help an SNP Government at Holyrood which has done nothing but agitate for the break up of the country for the last four years.
"Voters at this election have to ask themselves whether this is a party they can trust with the Union.
"The Scottish Conservatives have been clear we will do no deals that would put the UK at risk and every vote cast for the Scottish Conservative and Unionist party is a vote for our United Kingdom."
Ms Davidson ruled out a deal between the Tories and SNP at Holyrood.
The Scottish Conservatives and SNP worked together closely when Alex Salmond led a minority government between 2007 and 2011.
He relied on Conservative votes to get his budgets passed, supporting Tory policies to cut business taxes, increase the number of police officers and improve run-down town centres in return.
Polls suggest the SNP is on course to win a third term in office when Scots vote in May next year.
However, the Holyrood system, a mixture of first-past-the-post and proportional voting, is designed to prevent any one party gaining a majority.
In 2011, the SNP won 69 of the parliament's 129 seats with a 45 per cent share of the vote.
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