Milorad Dodik's party declared victory in the elections in Republika Srpska, the Serb entity of Bosnia and Herzegovina.
Nationalist parties also scored victories in other parts of the country, results that could keep tensions high both in Bosnia and Herzegovina and in the region.
"We have won," Dodik told his supporters in Banja Luka late Sunday.
According to him, preliminary results show that the Alliance of Independent Social Democrats, SNSD, will remain in power in Republika Srpska.
Citizens voted on October 4 for the tripartite Presidency and Parliament of Bosnia and Herzegovina, as well as for legislative bodies at other levels, including the Assembly of Republika Srpska.
This complex political system stems from the Dayton Agreement, which ended the 1992-1995 war.
According to this agreement, Bosnia and Herzegovina was divided into two entities with broad autonomy – Republika Srpska and the Federation of Bosnia and Herzegovina, with Bosniak and Croat majorities.
Both are connected through central state institutions, which have often functioned with difficulty.
In his post-election speech, pro-Russian politician Dodik said that, based on the results after 92 percent of the votes were counted, SNSD candidate Zhelka Cvijanovic would become a member of the tripartite Presidency of Bosnia and Herzegovina.
The current pro-Western member of the Presidency, Denis Beqirović, is expected to win the Bosniak seat.
They are expected to be joined by Darijana Filipović from the Croatian Democratic Union (HDZ), who is expected to win the Croatian seat.
At the age of 39, Filipović is expected to become the youngest member of the Presidency of Bosnia and Herzegovina since the end of the 1992-1995 war.
