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 (SNP) 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.
The Prime Minister announced his plan in a speech in London.
He promised an in/out referendum on the UK's membership of the EU if the Conservatives win the next general election in 2015.
The party's manifesto will ask for a mandate to negotiate a "new settlement" for Britain in Europe, he said.
He wants a new EU treaty to reshape the 27-nation bloc, resolve the problems of the eurozone, allow the transfer of powers back from Brussels to national governments and make Europe's economy more competitive and its institutions more flexible and democratically accountable.
Mr Cameron said it was his "strong preference" to enact these changes for the whole EU, not just Britain alone.
But if other states are unwilling to go ahead with a new treaty, he said he is ready to renegotiate the UK's position to achieve a settlement "in which Britain can be more comfortable and all our countries can thrive".