President Aleksandar Vucic declared “victory” in the March 4 municipal election in Belgrade, as exit polls indicated that his ruling Serbian Progressive Party (SNS) won around 45 percent of the votes.
Preliminary results by the Ipsos polling agency and carried by state TV projected that the list of former Belgrade Mayor Dragan Djilas trailed with some 19 percent.
Two other lists passed the 5 percent threshold to win a seat in the 110-member Belgrade City Assembly, which appoints the city mayor for a four-year term.
"This is the best result ever in Belgrade," Vucic told supporters. "This victory wasn't easy to achieve."
Ipsos reported that the final turnout was 51.1 percent.
Official results are due on March 5.
The SNS party has held power in Belgrade since the current mayor, Sinisa Mali, was elected in 2014, but fractured opposition parties hoped to mount a challenge in the traditionally liberal city.
They have accused Vucic's party of intimidating opposition supporters, registering phony voters, and orchestrating negative coverage of political rivals in media outlets controlled by the SNS, which rejects the accusations.
The independent CESID monitoring agency said that it recorded a number of irregularities at polling stations, including collective voting.
But Zoran Lukic, the president of the City Election Commission, said that the vote was going smoothly and denied the allegations of irregularities.
Some 1.6 million eligible voters had to choose the Belgrade City Assembly from 24 electoral lists.
Members of the city assembly are elected on a closed party-list, proportional representation system.
In April 2017, Vucic won Serbia’s presidential election in the first round, confirming his domination of the Balkan country.
Vucic has faced accusations of stifling democratic freedoms through pressure on opponents and independent media since the SNS party rose to power in 2012 and he became prime minister in 2014. He rejects the charges.
A former nationalist, he has vowed to lead Serbia into the European Union, while at the same time seeking to maintain good relations with traditional ally Russia.