Serbian voters go to the polls Sunday to elect a new president with the incumbent Boris Tadic set for a landslide victory over his nationalist challenger Tomislav Nikolic.

Tadic came just ahead of Nikolic in the May 6 first round of presidential elections, in which the nationalist has accused his rival of "vote fraud".

The claims were dismissed both by Serbia's prosecutor and electoral officials but they have cast a shadow over the polls.

"The claims of electoral fraud... put behind everything that should have been discussed by presidential candidates," said analyst Marko Blagojevic.

Serbia's electoral commission had rejected Nikolic's complaints as unfounded, saying his Serbian Progressive Party (SNS) had failed to provide any proof of fraud.

The state attorney also dismissed the fraud allegations after a probe into the case.

However Nikolic protested that the probe was controlled by Tadic's party.

"I am ready this time to fight personally against any attempted vote fraud," Nikolic told reporters.

Tadic rejected the claims and his party accused Nikolic of "provoking violence that could lead the country into a chaos".

Analyst Vladimir Todoric said Nikolic's moves were a "strategy to create a false scandal with an aim to prepare grounds for a possible withdrawal from the electoral process or destabilise the country."

"We will see whether the strategy will backfire and punishment by voters" in the second round," Todoric said.

Recent surveys show Tadic leading with 58 percent support against Nikolic's 42 percent.

Tadic, 54, has been able to pull ahead in the race for a fresh five-year mandate as he won an important backing from the Socialists, the third biggest party in the Serbian parliament after legislative polls.

The incumbent president who brought a once politically and economically isolated Serbia to the doorstep of the European Union, is focusing his campaign on EU integration and economic development through support for agriculture.

"These elections are crucial for Serbia because the country will change on that day and the question is: for better or for worse?," Tadic said.

If re-elected, he has vowed that during what would be his third and last presidential mandate, Serbia, which received EU candidacy status in March, will start membership talks by the end of this year, with the aim of joining in five years.

Nikolic, 60, has also promised to stay on a pro-European course, but has campaigned on more populist promises, like a tax hike on the rich to be used to increase pensions and welfare payments.

He also plans to step up investments in agriculture and industry.

"We will examine all privatisation processes (of former state-run companies) in the past and give back to the people what is theirs," Nikolic has said.

What is clear is that the new president would have to introduce painful reforms in order to restore economic stability of the country where 24 percent of 7.5 million inhabitants are unemployed, one of the highest jobless rate in Europe.

He is also expected to boost further talks between Belgrade and Pristina aimed at improving relations between Serbia and its breakaway province Kosovo -- a key condition for its integration into the EU.

More than 6.7 million eligible voters will cast their ballot at more than 8.500 polling stations on Sunday from 7 a.m. (0500 GMT) until 8 p.m.

At least 1,500 international and local observers will monitor the vote.