BANJA LUKA, Bosnia (Reuters) - Bosnian Serbs on Sunday voted overwhelmingly to keep their national holiday in a referendum held despite ethnically divided Bosnia’s highest court ruling it illegal.

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Organizers in the autonomous Serb Republic part of Bosnia said that with 71 percent of the votes counted, 99.8 percent of voters had supported the Jan. 9 “Statehood Day” holiday, with turnout possibly as high as 60 percent.

Most of the region’s Muslim Bosniaks and Catholic Croatians oppose the holiday. It coincides with a Serbian Orthodox Christian festival and also marks the Serb territory’s 1992 secession from Bosnia, which triggered a bloody three-year war.

Serb Republic nationalist President Milorad Dodik, who has been accused of using the referendum to set the stage for a secession vote, said the vote would go down in history as the “day of Serb determination”.

“I am proud of the people of Republika Srpska, of all those who came out and voted,” Dodik said in Pale, the town near Sarajevo which was the headquarters of Bosnian Serb wartime President Radovan Karadzic, convicted of genocide in the Bosnian war in April.

Bosnia’s international peace envoy Valentin Inzko said the referendum was an attack against Bosnia’s constitutional order without precedent and that its results would not be legally valid.

The Sarajevo-based Constitutional Court had banned the referendum after finding that the holiday itself discriminated against the region’s Bosniaks and Croats.

Western diplomats have warned that it violates the 1995 Dayton peace accords that ended the Bosnian war and could prompt sanctions or criminal charges against the organizers.

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 voiced support.

Police said no incidents were reported during the vote.

The region’s government 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.

Talk of a new war has increased ethnic tensions but both Serb and Bosniak leaders have dismissed such rhetoric.

“There will be no war, nobody will destroy Republika Srpska,” said Bakir Izetbegovic, the Bosniak chairman of the country’s three-man inter-ethnic presidency.

But Izetbegovic said he believed that organizers of the illegal vote will be prosecuted, “it was just the matter of time”.

Dodik dismissed the possibility of criminal charges being filed against him. “Republika Srpska has nothing to fear,” he said.