"This sentencing cannot and does not have the right to influence the future of Republika Srpska, therefore I am calling on all political representatives of the Serbian people in Bosnia and Herzegovina, especially Republika Srpska, to fight for their republic and people, whose future could be call into question by this sentence," Nikolic said in a statement.
The Bosnian War erupted between Bosnian Muslims, Serbs and Croats when Bosnia and Herzegovina announced its secession from Yugoslavia in 1992. The war claimed the lives of over 100,000 people, and forced more than two million people from their homes.
The Republika Srpska is an administrative entity in Bosnia and Herzegovina, which was established in 1995 following the war.
Karadzic, 70, became the most high-profile defendant after the death of former Yugoslav President Slobodan Milosevic in 2006 before his trial concluded.