SCOTTISH nationalists reacted with anger to a claim by the President of the European Commission that an independent Scotland would find it "extremely difficult, if not impossible" to join the EU.
Jose Manuel Barroso said countries such as Spain – which faces its own secession demands from Catalan and Basque separatists – could veto its entry.
But senior Scottish National Party figures described his claims as "preposterous" and "nonsense".
It is the second major policy setback in a week for First Minister Alex Salmond, who has angrily accused Westminster of "bullying" and "anti-democratic" tactics after all three main parties ruled out independent Scotland using the pound.
Mr Barroso's comments come days after the main parties at Westminster ruled out an independent Scotland sharing the pound with the rest of the UK under a currency union.
Senior figures within the Yes campaign are now reportedly considering a plan B, which would see a fully independent Holyrood existing outside full currency union with the remainder of the UK.
Mr Barroso compared Scotland's ambition to the plight of Kosovo, once part of Yugoslavia, which has had its membership opposed by Spain, Cyprus, Greece, Romania and Slovakia.
Mr Barroso told BBC1's Andrew Marr Show: "Of course it will be extremely difficult to get the approval of all the other member states. "We have seen Spain has been opposing even the recognition of Kosovo, for instance. So it is to some extent a similar case ... and so I believe it's going to be extremely difficult, if not impossible – a new member state coming out of one of our countries – getting the agreement of the others."
But Scotland's Deputy First Minister Nicola Sturgeon said: "This is a preposterous assertion – as the ridiculous comparison with Kosovo illustrates. Scotland is already in the EU and has been for 40 years."
The Scottish Government has said it will negotiate Scotland's EU membership in the 18 months after the referendum. Scottish ministers want the talks to be hammered out from within the Union while Scotland remains part of the UK, according to the Government's White Paper on independence. The independence referendum will take place on September 18.