Serbian police said on Monday said they have detained at least 38 people who took part in a protest against reported widespread irregularities during a recent general ballot, which declared the governing populists winners of the parliamentary and local council elections.

Claiming election fraud, particularly in the capital, Belgrade, opposition group Serbia Against Violence has been staging protests since the December 17 elections while some politicians began a hunger strike.

On Sunday hundreds of protesters tried to enter Belgarde’s city council, breaking windows, before riot police pushed them back using tear gas, pepper spray and batons.

Senior police official Ivica Ivkovic said those detained are facing charges of inciting violent change of constitutional order, in reference to attempting to overthrow the government, and violent behaviour.

He added that eight officers were injured, several seriously.

The opposition said police beat up some of its supporters.

With more protests planned for later on Monday, police said they would not allow roads or bridges to be blocked in the capital.

Police “are ready and capable of countering any acts of violence with determination”, Mr Ivkovic said.

The country’s Serbian Progressive Party has denied rigging the vote and described the elections as fair, despite criticism from international monitors and local election observers.

President Aleksandar Vucic described Sunday’s protests as an attempt to overthrow the government with help from abroad, without specifying what he meant.

Serbia’s Prime Minister Ana Brnabic thanked Russia on Sunday for tipping off Serbia in advance of violent protests against election results.

Serbia is formally seeking membership of the European Union but the country has maintained close ties with Moscow and has refused to join western sanctions imposed on Russia over the war in Ukraine.

Mr Vucic’s party claimed victory in both the parliamentary and Belgrade city elections.

Serbia Against Violence, the ruling party’s main contender, said it was robbed of a win, especially in Belgrade.

Representatives of several international rights watchdogs observing the elections reported multiple irregularities during the vote, including cases of bought votes and ballot-box stuffing.

They also noted unjust conditions for opposition candidates due to media bias, abuse of public resources by the ruling party, and Mr Vucic dominating the ruling party’s campaign and media time allocated for candidates, despite not taking part in the elections himself.

Serbia Against Violence said on Thursday in a letter sent to EU institutions, officials and member nations that it would not recognise the elections’ outcome.

The alliance called on the EU to do the same and to initiate an investigation into the results.