Serbian President Aleksandar Vucic has claimed victory in snap parliamentary elections, saying his party is heading for an absolute majority.
His Serbian Progressive Party, or SNS, is set to win almost 47% of the vote, according to projections.
Opposition parties under the Serbia Against Violence (SPN) banner were well behind with around 23%.
But they claimed electoral fraud favouring the government, and called a protest for this evening.
Initial results projected the SNS had won more than half of the 250 seats in the National Assembly.
Mr Vucic hailed the results. “My job was to do everything in my power to secure an absolute majority,” he told supporters, although he himself was not running for election.
Wearing a grey sweater, he was flanked on one side by Prime Minister Ana Brnabic and on the other by controversial Bosnian Serb leader Milorad Dodik.
The loose opposition Serbia Against Violence alliance, or SPN, had hoped to win control of Belgrade in Sunday’s local elections.
It was formed after two mass shootings in May which sparked huge protests. The attacks killed 19 people, including 10 at a school in Belgrade.
Despite the SPN’s hopes, initial results showed Mr Vucic’s party slightly ahead in the capital.
In a statement, SPN claimed electoral fraud. The coalition said: “More than 40,000 non-residents were brought to Belgrade”.
It demanded the annulment of the vote in the capital, and called on supporters to protest on Monday evening.
Results overnight from Serbia’s 8,273 polling stations confirmed the ruling party’s lead.
The SNS has been in power since 2012 but there have been three elections in the past three years.
As well as voting for parliament, Serbians were deciding on Sunday who would control 65 local authorities.