Bosnians are voting in municipal elections marked by a battle in the Bosnian Serb half of the country between a pro-European Union coalition and the pro-Russia separatist party that has ruled that region for more than a decade.

Some 3 million voters will choose mayors and municipal councils in both of Bosnia's two semi-autonomous regions on Sunday.

Republika Srpska and the Bosniak-Croat Federation have their own governments, presidents and parliaments, but are linked by a set of shared state-level institutions.

Led by President Milorad Dodik, who has dominated the Bosnian Serb political scene for years but started to see political setbacks, the ruling party of Republika Srpska campaigned on a promise of Serb secession from Bosnia.

Dodik's opponents have focused on bread and butter issues while accusing him of corruption.