Belgrade  -  Serbia's pro-European and ultra-nationalist parties are tied ahead of May parliamentary elections, leaving nationalist caretaker Prime Minister Vojislav Kostunica as the potential kingmaker, a poll said Wednesday.

After Kostunica's government fell in March over Kosovo's declaration of independence from Serbia, the May 11 snap vote will test Serbs' interest in closer ties with the West.

Voters are about evenly split between pro-European President Boris Tadic's bloc and the ultra-nationalist Serbian Radical Party (SRS) at 35 per cent each, said a survey by Strategic pollsters quoted in Belgrade newspapers.

Nationalists led by Kostunica, who headed the Serbian government after December 2003 and January 2007 elections, got about 13-per-cent support, meaning they could again dictate the terms for a governing coalition.

The fiercely pro-Western Liberal-Democratic Party was polling about 9 per cent and the Socialists of late strongman Slobodan Milosevic some 6 per cent, the survey said.

In the blurry picture, Kostunica has the greatest potential to forge coalitions as he has already allied twice with Tadic's Democratic Party (DS). In recent years he has shifted toward the nationalist right, into the domain of the SRS.

"Now more than ever before it appears realistic that SRS and (Kostunica's) DSS would form the cabinet," Marko Blagojevic of the Centre for Free and Democratic Elections was quoted as saying.

The SRS won the most votes in the last two elections, but was stymied from leading the government because of its belligerent nationalism.

Its status on the Serbian political scene has however improved as the country polarized more sharply after Kosovo's secession.

Still, no clear winner is in sight and concern is rising that the bickering of Serbian parties will cost the country - which has already frozen its approach to EU membership - many more months.

On May 11, Serbs will also vote in municipal elections and for the government of Serbia's Vojvodina province. (dpa)