Serbian police on Saturday evening clashed with anti-government protesters demanding snap elections and an end to the 12-year rule of President Aleksandar Vucic.

Police deployed scores of officers in riot gear around government buildings, parliament and nearby Pionirski Park, where throngs of Vucic's backers from across the country gathered in a counter-protest.

After the protest ended at around 10 p.m. (2000 GMT), some protesters who wanted to confront Vucic's backers threw bottles, rocks and flares at the police, who used force to disperse them in several locations across Belgrade's city centre.

The protesters shouted: "Keep the shields down," calling on the police to stop intervening.

Police detained several dozen protesters, while six police officers were reported injured in clashes, Dragan Vasiljevic, the director of police, told a press conference late on Saturday.

Vucic said protesters attempted to topple the state. "They (protesters) wanted to topple Serbia, and they have failed," he wrote on his Instagram page.

In a statement, students accused the government of an escalation of tensions.

"They (authorities) ... opted for violence and repression against the people. Every radicalisation of the situation is their responsibility," students wrote on the X social network.

In a statement, Ivica Dacic, the interior minister, said police will act to maintain public order.

"The police will take all measures to establish public order and peace, ... and apply all its powers to repel attacks, and arrest all those who attacked the police," Dacic said.

Months of protests across the country, including university shutdowns, have rattled Vucic, a populist, whose second term ends in 2027, when there are also parliamentary elections scheduled.

Vucic's opponents accuse him and his allies of ties to organised crime, violence against rivals and curbing media freedoms, something they deny.

The protesters, who want the government to heed their demands by the end of the protest, have pledged non-violence.

Vucic has previously refused snap elections. His Progressive Party-led coalition holds 156 of 250 parliamentary seats.

Earlier on Saturday, Vucic said unspecified "foreign powers" were behind the protest. He said police should be restrained, but warned that violence will not be tolerated.

“The country will be defended, and thugs will face justice,” he told reporters in Belgrade.

Sladjana Lojanovic, 37, a farmer from the town of Sid in the north, said she came to support students.

"The institutions have been usurped and ... there is a lot of corruption. Elections are the solution, but I don't think he (Vucic) will want to go peacefully," she told Reuters.

In the days ahead of the protest, police arrested about a dozen anti-government activists, charging them with undermining the constitution and terrorism. All denied the charges.

Protests by students, opposition, teachers, workers and farmers began last December after 16 people died on November 1 in a Novi Sad railway station roof collapse. Protesters blame corruption for the disaster.

The Belgrade rally coincides with St. Vitus Day, venerated by most Serbs, which marks the 1389 Battle of Kosovo with Ottoman Turks.