David Cameron's European Union referendum speech has "completely changed" the debate in Scotland ahead of the 2014 independence referendum, according to First Minister Alex Salmond.
The Scottish National Party leader said Eurosceptics in the Prime Minister's Conservative Party pose the biggest threat to Scotland's position in the EU.
"This was a fundamentally confused speech by the Prime Minister, which is painfully short on detail," said Mr Salmond in a statement.
"On the one hand he is trying to appease the Eurosceptics on his own backbenches and on the other he is trying to appear as a European reformer.
"He is trying to ride two horses at the same time and it is inevitable he will fall off before long.
"This completely changes the nature of the debate in Scotland.
"The Westminster parties have consistently claimed that a referendum on Scotland's independence causes uncertainty.
"It is now clear the persistent undercurrent of Tory Euroscepticism poses the biggest threat to Scotland's position in the EU and has now helped to hole below the waterline the baseless scaremongering of Alistair Darling and the rest of the No campaign."
Mr Darling, the Labour MP and former Chancellor, leads the Better Together pro-UK campaign group.
Scotland will decide in autumn next year whether to leave the UK and become an independent state, and by extension a full member of the EU in its own right.
One argument in the pro-UK camp is that Scotland's place in the EU is uncertain if voters opt for independence in 2014.
Mr Cameron's European referendum plan raises the prospect that Scotland could choose to stay in the UK but later find itself out of the EU after a vote in 2017.
Meanwhile, Deputy First Minister Nicola Sturgeon revealed that her call for early talks with the European Commission (EC) on an independent Scotland's place in the EU have been declined.
EC vice-president Maros Sefcovic wrote to her saying that president Jose Manuel Barroso has not and will not comment on any specific situation relating to any one member state.
Last month Mr Barroso said it was "obvious" that a newly independent state would need to apply for membership - a comment widely used to support claims Scotland would not enjoy a smooth transition.
Ms Sturgeon wrote today: "The commission have moved back into neutral gear.
"The letter goes on to argue that since they don't have a position on a particular case then there is nothing usefully to be gained from a meeting at this stage. That's a pity since the world has moved on even since December."