BELGRADE, January 21 (RIA Novosti) - Serbia is set to hold a runoff between the top two presidential contenders after an ultranationalist candidate narrowly won the first round of voting, election authorities said on Monday.

With 98.68% of votes counted Tomislav Nikolic, deputy chairman of Serbia's ultranationalist Radical Party, won 39.96% in the first round. Pro-Western incumbent leader Boris Tadic received 35.41%, and other candidates garnered less than 10%.

According to Serbian law, if no candidate gains more than 50%, the leading two contenders must compete in a runoff, which has been scheduled for February 3.

The third and fourth-placed candidates in the first voting round share Nikolic's hard-line stance on many key foreign policy issues, putting him in a strong position for the runoff, according to analysts.

Both Tadic and Nikolic staunchly oppose independence for Serbia's breakaway province of Kosovo.

In the first round a total of 1.91% of ballot papers were declared invalid. Voter turnout was around 61.5%, higher than in recent elections. The final results of the first round will be announced by 7 p.m. GMT today.