Supporters of the ruling Serbian Progressive Party (SNS) threw flares and firecrackers at anti-government protesters in Novi Sad on Wednesday evening, according to Reuters, prompting police to intervene to end the standoff, a major escalation of nine-month-long protests in Serbia.

Daily protests countrywide in Serbia, following the deaths of 16 people, killed when a roof on a renovated railway station in Novi Sad collapsed last November, have rattled the popularity of populist President Aleksandar Vucic and SNS.

At a news conference late on Wednesday, Vucic, flanked by Interior Minister Ivica Dacic, said 16 police officers and around 60 SNS backers have been injured in Novi Sad. He also accused unidentified foreign powers of orchestrating riots and pledged arrests.

"Persons who violated the law will be apprehended ... Tonight, we have averted a catastrophic scenario planned by someone from abroad," he said.

Reuters could not independently verify Vucic's claims.

Footage by private N1 TV showed flares and firecrackers being thrown at protesters in Novi Sad from the direction of the SNS offices. It also showed anti-government protesters, some with bloody faces, saying Vucic's backers used sticks and truncheons to attack them.

Opposition Move-Change movement said Vucic's loyalists have been responsible for the clashes.

"Attacks on people with pyrotechnic devices violate their right to life and protest," it said in a statement.

In the capital city of Belgrade, police in full riot gear blocked anti-government protesters from approaching the area in a park near the parliament building where Vucic's supporters have been camping since March.

Elsewhere in Belgrade, anti-government protesters clashed with police who prevented them from approaching local SNS offices.

The protesters have blamed corruption for the Novi Sad railway roof collapse and have demanded early elections that they hope would remove Vucic and his party from power after 13 years.

Students, opposition, and anti-corruption watchdogs have accused Vucic and his allies of ties to organised crime, violence against rivals and curbing media freedoms, something they deny.

On Wednesday evening, students who are leading the protests called supporters to protest in front of SNS offices in major cities in Serbia, including Belgrade, Novi Sad, Kragujevac, Cacak and Nis, after several protesters were injured in clashes with SNS in the town of Vrbas on Tuesday evening.

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