Austria blocked European Union agreement today on a mandate to start entry negotiations with Turkey next week.
The development means EU foreign ministers will have to hold an emergency meeting on Sunday, the eve of the talks to seek a deal.
A 24-1 deadlock at a meeting of EU ambassadors means Turkey will be kept on tenterhooks up to the hours before Foreign Minister Abdullah Gul is due to fly to Luxembourg to begin the talks.
Diplomats said Austria stuck to its demand that Turkey be offered an explicit alternative to full membership - something Ankara rejects - but was isolated.
Chancellor Wolfgang Schuessel also demanded the EU open talks immediately with Croatia, Austria's historic ally and Roman Catholic neighbour.
Those negotiations, due to start in March, have been frozen because of Zagreb's failure to satisfy a UN war crimes tribunal.