The rally, the largest since the elections, marked the culmination of nearly two weeks of demonstrations against alleged widespread irregularities in the vote. International observers have also raised concerns about the fairness of the election.
Vucic's Serbian Progressive Party (SNS) was declared the winner with 46.72% of the votes, but the main opposition alliance, Serbia Against Violence, claims the election was stolen, particularly in Belgrade.
Demonstrators waved Serbian flags and chanted slogans such as "We do not accept!" and "These elections must be annulled." They were joined by opposition leader Marinika Tepic, who has been on a hunger strike since December 18 in protest of the results.
"These elections must be annulled," a frail-looking Tepic told the crowd from the stage. "We will not give up until our demands are met."
Tepic's health has reportedly been deteriorating, and she was expected to be hospitalized after appearing at the rally.
Serbia Against Violence has led daily protests since the elections, demanding a rerun of the vote. Tensions have risen in recent days, with violent incidents and arrests of opposition supporters at a protest last weekend.
The protest was also supported by student organizations and a group of public figures called ProGlas, which means "pro-vote."
Serbia Against Violence came second in the election with 23.56% of the vote. The Socialist Party of Serbia was third with 6.56%.
The Organization for Security and Co-operation in Europe (OSCE) has said that the elections were "generally well-organized," but it also raised concerns about "pressure on voters, smear campaigns, and the misuse of state resources."
The European Union has called for all sides to "engage in constructive dialogue" to resolve the crisis.
It remains to be seen whether the protests will lead to any changes in the election results. However, they have undoubtedly cast a shadow over Vucic's victory and raised concerns about the state of democracy in Serbia. (ILKHA)