Serbs re-elected Tadic -- who based his election campaign on fostering pro-European sentiments -- with a slim 51.1 percent majority on Sunday, Feb. 3.

On Wednesday, however, Serbian Prime Minister Vojislav Kostunica blocked a cabinet meeting on the signing of a trade, travel and education pact with the EU.

The move was seen as a blow to the already fragile coalition government in which Kostunica's conservative Democratic Party of Serbia (DSS) is the weaker partner to Tadic's pro-European Democratic Party.

"In order to preserve the stability of the state, it is necessary that all state institutions do their job and no one is allowed to obstruct the work of state institutions due to their party positions," Tadic said in a statement in which he urged Kostunica to convene the meeting.

EU deal seen as dishonest

The EU had offered Serbia a deal which included political dialogue, free trade, visa relaxation and educational cooperation.

Kostunica believes the EU offer was aimed at securing Belgrade's "assent for Kosovo's independence." The Albanian-majority province is expected to declare independence from Serbia, with the support of most EU nations, in a matter of weeks.

On Monday, the EU approved a police and justice mission to Kosovo, which deepened disagreements within Serbia's coalition government. Kostunica saw the move as another step towards Kosovo's independence.

The EU has denied that the cooperation deal is related to Kosovo. The European Commission confirmed Wednesday that the signing, scheduled for Thursday, would not happen and criticized the "obstruction" of Kostunica.

"I very much regret we have to postpone tomorrow's signing of the political agreement, of course the EU commitment is firm and the invitation remains on the table," EU Enlargement Commisioner Olli Rehn told reporters Wednesday.

EU unhappy about delay

"It is... sad for Serbia if politicians continue to put power games ahead of their own citizens' interests," added Rehn, who has been a strong proponent of future EU membership for Belgrade.

EU foreign ministers had made the offer last week as a show of goodwill about the country's future membership in the bloc. Yet the EU deal was made after failing to go ahead with a broader Stabilization and Association Agreement (SAA).

The SAA, the first formal step to EU membership, was blocked by the Netherlands over Serbia's failure to capture fugitives of the UN war crimes tribunal.