Fresh clashes erupted between anti-government protesters and riot police across Serbia in the fifth night of unrest in a row, after offices of the the ruling Serbian Progressive Party (SNS) were set on fire, BBC reported.

Police in Valjevo reportedly used stun grenades and tear gas on protesters after a small group of masked people attacked the empty facilities of the SNS, setting them on fire.

There were widespread allegations of violence and police brutality in the capital, Belgrade, and Novi Sad. Serbia's interior ministry has denied these allegations, according to BBC.

It comes as Russia pledged to shore up the beleaguered pro-Moscow President Aleksandar Vučić, who leads the SNS, saying it would not "remain unresponsive".