A pro-Western coalition determined to bring Serbia into the European Union made a surprisingly strong showing in parliamentary elections, but faced the specter of a protracted power struggle with rivals who vowed to join forces to form a government.

The challenge cast a shadow over President Boris Tadic's claim of victory in Sunday's vote, and triggered fresh political turmoil in a country divided over whether it should join the EU or shift toward its traditional ally Russia and revert to its nationalist past.

Tadic proclaimed "a great day for Serbia" after projections by an independent monitoring group and partial results from the state electoral commission gave his Coalition for a European Serbia a 10 percent lead over the ultranationalist Radical Party.

"The citizens of Serbia have confirmed Serbia's European path," he said. "Serbia will be in the European Union. We have promised that, and we will fulfill that."

But leader of the ultranationalist Radical party, Tomislav Nikolic, urged his allies to pull together.

Nikolic said he would meet Monday with Prime Minister Vojislav Kostunica's conservative coalition and former Serbian strongman Slobodan Milosevic's Socialists to form a government.

Any alliance that can muster a simple 126-seat majority in the 250-seat parliament can govern. Although Tadic's coalition appeared assured of 103 seats, the Radicals were poised to get 76 seats. If they joined forces with Kostunica's bloc and the Socialists, their combined strength would be 127 seats.

Nikolic also accused Tadic of inciting violence by proclaiming victory. Tadic, in turn, made clear he saw Sunday's outcome as a mandate to take the country into the EU. He, too, was expected to court the Socialists, with 21 seats, in an attempt to support his government.

The European Union called the success of Tadic's coalition a "clear victory" by pro-European forces.

Tadic's opponents said their own vote tabulations confirmed the pro-Western forces' victory _ an astonishing turnaround after weeks of speculation that the Radicals and Kostunica together would sweep to victory.

Kostunica said Sunday evening his differences with Tadic's coalition were "insurmountable," and that he was open to talks with the Radicals.

Official results were not expected until Monday, but the state electoral commission issued partial results that corresponded to the projections of the Center for Free Elections and Democracy and the tabulations of the main parties.

The respected center, whose representatives observed vote tallying at polling stations across Serbia, said Tadic's bloc had 39 percent. It said the Radicals were running a distant second with 28.6 percent, and that Kostunica's bloc had about 11.6 percent. The Socialists had about 8.2 percent _ their best result since Milosevic's ouster in 2000.

The pro-Western coalition's surprisingly strong showing came just three months after protesters outraged by Kosovo's Feb. 17 independence declaration set fire to part of the U.S. Embassy in Belgrade.

That anger had stoked expectations of an electoral backlash and a Radical victory that would have squelched Serbia's efforts to prepare for eventual EU membership. The Radicals had vowed to steer the country away from the West, where many key powers recognized Kosovo, and toward Russia.

Serbs consider Kosovo the heart of their ancient homeland and Serbian Orthodox faith, and their bitterness has nudged the country toward ultranationalists promising to restore bruised national pride.

Tadic, who also opposes Kosovo's independence, reiterated Sunday that he would never recognize its statehood.

He has been publicly denounced as a traitor for signing a pre-entry aid and trade pact with the EU _ a deal that Kostunica and Nikolic contend amounts to blood money in exchange for giving up Kosovo.

Milosevic was ousted by a pro-democracy movement in 2000, and the former leader _ who presided over the bloody 1990s breakup of Yugoslavia _ died in March 2006 in a prison cell in The Hague, Netherlands, where a U.N. tribunal was trying him for atrocities in the Balkans.

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Associated Press writers William J. Kole and Dusan Stojanovic contributed to this report.