SARAJEVO (Reuters) - The largest Serb party in Bosnia said on Saturday it would push for a referendum on independence for the country’s autonomous Serb Republic in 2018, setting it on a collision course with the West, unless the region is granted greater powers.

Zeljka Cvijanovic (L-R), Prime Minister of Republika Srpska, Milorad Dodik, leader of Alliance of Independent Social Democrats party (SNSD), and members of party, Nebojsa Radmanovic and Nikola Spiric, vote during the congress of the party in East Sarajevo, April 25, 2015. REUTERS/Dado Ruvic

The threat represents potentially the greatest challenge to Bosnian statehood since it split from federal Yugoslavia and descended into war that killed 100,000 people from 1992 to 1995.

The SNSD party, which is led by the Republic’s nationalist president Milorad Dodik, adopted a resolution making the independence threat official party policy.

Dodik accuses state authorities in Bosnia of trying to usurp autonomous powers granted to the Serb Republic under a U.S.-brokered peace deal.

“The Serb Republic cannot accept any further takeover of its authorities by the state under the guise of reform,” he told reporters after an SNSD convention.

The resolution states that unless the Serb Republic is able to strengthen its autonomy by the end of 2017, the regional assembly, in which SNSD currently holds a majority, will call a referendum to break from the Bosniak-Croat Federation, the other half of Bosnia.

“Based on the referendum results, the Serb Republic authorities... will propose to the Federation a peaceful dissolution and mutual recognition,” it said, adding that the region would pursue membership of the European Union.

In response, the office of Bosnia’s international peace overseer, who has the power to fire officials and overturn laws, said that under the 1995 peace accord, neither entity has the right to secede. “No party paper can change these facts,” it said in a statement.

REFORM IMPASSE

Dodik argued that the Serb Republic’s own constitution and laws left room for self-determination.

He has long advocated Bosnia’s dissolution, putting him at odds with Western powers that have invested thousands of troops and billions of euros in securing sovereignty for the Balkan state.

Leaders of Bosnia’s Muslim Bosniaks, Orthodox Serbs and Catholic Croats share little common vision of their country’s future, frustrating reform efforts and progress toward the European mainstream.

While the Bosniaks want a strong, more centralized state, Serbs are fiercely defensive of their autonomy and some Croats want their own entity.

The SNSD resolution has the potential to undermine a new EU initiative to spur economic and political reform in Bosnia after years of stagnation that triggered unprecedented civil unrest in February last year.

Analysts speculate that Dodik has been emboldened by events in Ukraine and Russia’s annexation of Crimea. He has also grown increasingly assertive since an election in October last year that shook his eight-year hold on power.