Nicola Sturgeon has told ITV News that the Conservatives "don't deserve to be the Government" if they are unable to command a majority at the General Election.
The SNP leader reiterated that her party would not take part in any "working arrangement" with David Cameron's party in the event of a hung parliament, and said her MPs would take action to stop a Tory minority government "even getting off the ground".
She said: "We'd vote in a motion of confidence to stop David Cameron getting back into Downing Street."
Sturgeon's comments follow remarks she made during yesterday's SNP spring party conference where she made a direct appeal to Labour to "join forces with us" in a bid to keep the Conservatives out of government after the General Election.
Labour have not commented on the appeal directly but Scottish Labour leader Jim Murphy appeared to dismiss the idea that the SNP would be able to "shake-up" Westminster to the benefit of other nations in the United Kingdom.
He said: “Despite all the cheering and backslapping the facts remain only Labour or the Tories can form the next UK government."