Serbian nationalist leader Tomislav Nikolic, who faces incumbent president Boris Tadic in a May 20 presidential run-off, on Saturday called on his supporters to protest against alleged election fraud.
Nikolic said his Serbian Progressive Party (SNS) "will organise from tomorrow (Sunday) peaceful, non-violent democratic protests to show that the elections were not held in accordance with the law," Beta news agency quoted Nikolic as saying.
Speaking after the meeting of his party's leadership in Belgrade, Nikolic insisted the SNS would not recognise the May 6 poll results as given by Serbia's official electoral commission.
On Thursday, Nikolic accused Tadic and his Democratic Party (DS) of " brutal electoral fraud" at the presidential and parliamentary polls last Sunday.
Nikolic showed reporters a bag he claimed was filled with ballot papers from one polling station in Sunday's election that were found in the bin.
He said extra voting forms had also been printed and used by Tadic's party for ballot stuffing.
International observers, including those from the Council of Europe and the Organization for Security and Cooperation in Europe (OSCE), said Monday the elections were free and fair.
The electoral commission meanwhile rejected a complaint filed to it by Nikolic's party, citing a "lack of evidence."
The complaint had "no elements needed to determine what kind of irregularities were committed," a commission official said.
Incumbent Tadic, who had earlier rejected the claims of alleged fraud as "insinuations," warned the opposition's call for protest was a "call for destabilisation" of the country and urged calm.
"The institutions should do their job and verify results of the elections while all those taking part in the electoral course should contribute to a calm atmosphere," Tadic said, according to the state television RTS.
Nikolic, whose party became the strongest single force in the future assembly and declared victory following the announcement of the results, changed tack after Tadic announced a coalition with the third-ranked Socialist party which would also support him in the presidential run-off.
A poll published on Friday showed Tadic is set for a landslide victory over his nationalist rival in the second round.