Months of anti-government rallies in Serbia lapsed into violence again as supporters of President Aleksandar Vucic clashed with his opponents in three of the Balkan country’s biggest cities.

President Aleksandar Vucic is facing accusations of sending hooligan groups to suppress the anti-corruption movement that has shaken the country for the past nine months.

Serbia’s police said they detained hundreds of demonstrators who took part in anti-government protests throughout the country this week. The arrests came amid reports of police brutality and excessive use of force during the unrest.