Serbian police say they have detained at least 38 people who took part in protests following reports of irregularities, including vote-buying, in the December 17 election.
The detainees are suspected of violent behavior and of having tried to overthrow the government.
On Christmas Eve, protesters tried to storm the city council building in the capital Belgrade, using eggs, flagpoles and stones.
Eight police officers are said to have been injured in clashes, where the police used pepper spray, among other things.
During Christmas Day, the protests continued. Hundreds of university students took part in a protest that blocked roads in Belgrade. The protests seem to have been peaceful so far, although the police warned that they were prepared to respond decisively to “all forms of violence”.