A pro-EU alliance emerged today as the biggest party after Serbia's snap general election, but it may have to rely on the support of the late Slobodan Milosevic's Socialist Party, in order to form a government in an extraordinary demonstration of the complexity of Balkan politics.

Boris Tadic, the reformist President of Serbia, hailed his party's 39 per cent share of the vote as a victory for modernising forces that see the country's future as a member of the European Union, after an election triggered when the province of Kosovo declared independence in February.

Despite his better-than-expected showing at the polls, however, Mr Tadic was warned by his nationalist rivals that they could still build an anti-EU coalition to keep his Democrat Party from office as a frantic round of power-sharing talks began today.

The size of support for the Democrats suggested that the nationalists had failed in their attempt to turn Serbia back towards its traditional ally, Russia, and away from the path towards the EU by playing on wounded national pride over the loss of Kosovo.

Tomislav Nikolic, leader of the Radicals — the main nationalist party that won 29 per cent of the vote — ominously told Mr Tadic that he risked provoking violence by his early declaration of victory last night before the five main party groupings had a chance to thrash out a coalition government.

The Socialist Party gained about 8 per cent to emerge as the key players in the post-election bargaining. It would be king-maker if it sided with the nationalist bloc of the Radicals and the party of Vojislav Kostunica, the former Prime Minister, or if it jumped into bed with Mr Tadic and another small pro-Western group.

The horse-trading left last night's proclamation by senior EU figures that the election was a clear vote for the pro-Western reformists looking somewhat premature. These factions are left in the uncomfortable position of having to court the party founded by Milosevic, which insists that it has moved on from its war-mongering nationalist days, despite quoting him at its campaign rallies.

While the Socialist Party would seem an unlikely partner for a government that wants Serbia to join the EU, the lure of power and seats in the Cabinet may be too hard to resist - but the price demanded might make uncomfortable reading in Brussels. There has been speculation that the Socialists could argue for allowing the return from exile in Russia of Milosevic's widow, Mira Markovic, or his son Marko Milosevic.

Senior EU figures insisted that the 39 per cent showing by Mr Tadic's Democrats pointed to a European future.

Olli Rehn, the EU's enlargement commissioner, said: “The Commission takes note of the preliminary election results and welcomes the success of the reformist forces that share European values. This should enable swiftly forming a new government.

“I trust the new Government will pursue the country's reform agenda and its path towards the EU. Serbia can become the engine of the Western Balkans and the EU is ready to accelerate its EU course - including candidate status.”

Mr Nikolic said: “There is a possible coalition without the Democratic Party and we warn Serbia about that.”

Ivica Dacic, leader of the Socialists, said: “They all have my number, I will be expecting their call.”

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