BELGRADE (Reuters) -Serbian police detained 79 protesters late on Wednesday in a crackdown on street demonstrators calling for a snap election and an end of the 12-year rule of the President Aleksandar Vucic and his Serbian Progressive Party.

Police and protesters clashed in the capital Belgrade and the cities of Novi Sad, Nis and Novi Pazar, the interior ministry said in the statement on Thursday.

Months of protests across Serbia, including university shutdowns, have rattled Vucic, a former ultranationalist who converted to the cause of European Union membership in 2008.

His second term ends in 2027, when parliamentary elections are also scheduled. 

The protesters launched blockades of major junctions and roads in Belgrade and other towns across Serbia on Sunday over the arrest of activists when police and demonstrators clashed at a big opposition rally on Saturday.

On Wednesday evening, police moved to remove students in front of the entrance of the Law Faculty in Belgrade, and briefly detained dozens, N1 TV reported.

Oliver Stojkovic, a professor at the medical faculty, told Fonet news agency that four students had been injured in the police action and taken to hospital.

"This (the police action) is an absolute violation of human rights and a violation of the freedom of the university," Bozo Prelevic, a former interior minister, told Reuters.

The U.N. human rights office said on X it was "closely monitoring situation after reports of violence, harassment & arbitrary detention of protesters" and urged authorities to exercise restraint.

Vucic's opponents accuse him and his allies of ties to organised crime, violence against rivals and curbing media freedoms. Vucic denies the accusations.

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.

(Reporting by Ivana SekularacEditing by Ros Russell)