Serbian police clashed with anti-government protesters in Belgrade Saturday night as the demonstrators demanded snap elections and an end to the 12-year rule of President Aleksandar Vučić.

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.

Months of protests in Serbia began in December after the awning of the main train station in Novi Sad, Serbia’s northern regional capital, collapsed and killed 14 people. Protesters blame corruption for the disaster, which has triggered the most visible and wide-reaching protest movement in modern Serbian history.

Saturday’s protest ended around 10 p.m., when some anti-government protesters moved to confront a counter-protest of Vučić’s backers, Reuters reported.

Police deployed scores of officers in riot gear around government buildings, parliament and nearby Pionirski Park. Protesters threw bottles, rocks and flares at the police, who used force to disperse them in several locations across Belgrade’s city center, according to media reports.

President Vučić wrote on his Instagram page that “you cannot defeat Serbia with violence”, and in a separate post commended police for their “patriotic, serious approach” to “defeat the attackers with minimal use of force.”

Almost 50 officers and more than 20 civilians were injured, Interior Minister Ivica Dačić told reporters in Belgrade on Sunday, Bloomberg reported.

Dačić condemned the violence, saying “police will take all measures to restore public order and peace and will repel all attacks.” After 77 protesters were arrested overnight, 38 remain behind bars pending criminal or misdemeanor charges, he said.

In a statement, students leading the protests accused the government of escalating of tensions. “They (authorities) … opted for violence and repression against the people. Every radicalization of the situation is their responsibility,” they wrote.