Bosnia’s ethnic Serbs have begun voting in a referendum over a disputed national holiday, defying a ban by the country’s highest court and western pressure to call off a process that risks stoking ethnic tensions in the divided Balkan country.

The referendum, on whether to mark January 9 as “Statehood Day” in the Serb Republic part of Bosnia, on Sunday is the first since a 1992 vote on secession from Yugoslavia that ignited three years of conflict in which 100,000 were killed.

Polling stations across the predominantly Serb region in Bosnia opened at 05:00 GMT and will close at 17:00 GMT. Organisers said the first preliminary results were expected within 48 hours after the vote.

“I came to vote because every nation and every state has its own national holiday. Accordingly, our Serbian people must have their holiday,” said Vojo Vujakovic, 60, at a polling station near the Bosnian Serb capital of Banja Luka.

Novak Kajkut, another voter in the city, said: “We don’t dispute the right of the Muslim Bosniaks to mark their holidays but they can neither dispute this right to us”.

The Sarajevo-based Constitutional Court has ruled that the holiday would be illegal because it coincides with a Serbian Orthodox Christian holiday and so discriminates against Muslim Bosniaks and Catholic Croats living in the Serb Republic. The court also banned the referendum.

January 9 is the date when Bosnian Serbs declared independence from Bosnia in 1992, precipitating the country’s devastating war marked by mass killings and persecution of Bosniaks and Croats in Serbian territory. It was Europe’s bloodiest conflict since World War II.

Many believe that by defying the court ruling, Bosnian Serb leader Milorad Dodik is aiming to highlight the weakness of post-war Bosnia’s central authorities in Sarajevo and set the stage for a vote on secession.

“The Republic is going into a referendum. It’s a great day for our Republic and our people,” Dodik said on Friday after a trip to Moscow, where he met Russian President Vladimir Putin.

“We have to show our dignity, that we are a democratic people and that we have the right to make our own decisions,” he said.

WATCH: Bosnia – divided country, divided media

The Serb region’s administration has said it would comply with the court’s ruling on the “Statehood Day” and make changes to its law on holidays to ensure it was not discriminating against other peoples – but only after the vote.

The Serbs celebrate the holiday by hanging out Serb flags and holding Orthodox Christian ceremonies in public institutions, which non-Serbs say is aimed at excluding them.

Western diplomats warn that the referendum violates the 1995 Dayton peace accords that ended the Bosnian war.

Some Bosniak politicians said that it would weaken Bosnia’s delicate structure, created to hold the country together in the aftermath of the devastating war. Many in the Bosniak and Croat- dominated autonomous region fear that the Serb Republic could be preparing to secede.

Talk of a new conflict has increased tensions, prompting the Serb Republic police to raise the security level at the weekend.

“What’s happening brings back memories of what happened in 1992,” when the Bosnian war began, said Nusreta Sivac, a Bosniak who was held in a Serb detention camp in the western town of Prijedor during the war.

While the United States, which brokered the Dayton treaty, and the European Union called on the Serb Republic to cancel the vote, fearing instability, Russia supported the plebiscite.

“The West and Russia are choosing sides again – whenever big powers get involved, people suffer,” Bosnian Serb opposition leader Mladen Bosic told Reuters news agency.