Thousands gathered in a square in in central Belgrade on Saturday in the biggest protest yet over parliamentary and municipal elections on December 17, results of which the demonstrators want annulled.

Protesters waving Serbian flags and holding a banner reading “We do not accept” cheered Marinika Tepic, a leader of the opposition Serbia Against Violence alliance, who has been on hunger strike since December 18, Reuters reported.

The ruling Serbian Progressive Party (SNS) won 46.72% of the votes in the Dec. 17 snap parliamentary election, according to preliminary results from the state election commission.

“These elections must be annulled,” Tepic, who came to the stage with the help of two colleagues, told the protesters, gathered in front of the landmark Moskva hotel.

Serbia Against Violence, which placed second in the general election, has accused the SNS of widespread vote fraud, which the authorities deny.

The Saturday protest was supported by students’ organizations and by an initiative gathering public figures including prominent intellectuals and actors dubbed ProGlas.