Ukraine's Supreme Court has blocked the inauguration as president of Prime Minister Viktor Yanukovich, whose contested election has led to mass protests.
The court is to examine a complaint from the country's Opposition over the conduct of the election commission overseeing the disputed presidential election.
The court rejected the official publication of election results that showed Mr Yanukovich had beaten Viktor Yushchenko last Sunday.
A president cannot be sworn in without the result being officially published.
The decision came as thousands of opposition supporters protested for a fourth day in sub-zero temperatures in the capital, Kiev, to support Mr Yushchenko, who called for a nationwide strike.
Mr Yushchenko's supporters have said major roads throughout Ukraine had been blocked as part of a campaign of civil disobedience, up to and including a general strike.
However, miners in the Russian-speaking east of the country, which supports Mr Yanukovich, say they will continue working.
Ukraine's crisis has overshadowed an EU-Russia summit at The Hague. At the end of the summit, the EU said it did not accept the election result.
The union said the poll fell short of international standards. In a statement, rotating EU president the Netherlands said that Ukrainian authorities must remedy irregularities reported by international election observers.
However, the Russian President, Vladimir Putin, said it was up to the Ukrainian courts to resolve any disputes over the election. Mr Putin has already congratulated Mr Yanukovich for winning.
The outgoing President Leonid Kuchma has warned that Ukraine could plunge into civil war.
