SARAJEVO, Bosnia-Herzegovina (AP) — Bosnia’s election authorities expressed concerns Friday over widespread problems at polling stations and reports of irregularities and vote-rigging in the general election last weekend. They ordered ballot checks at over 1,000 polling stations and promised to investigate all potential failings before certifying the results of the vote.

Members of the country’s central, multi-ethnic election commission shared their concerns a day after thousands of people protested in Banja Luka, the main city in Bosnia’s Serb-run part, alleging that a pro-Russia Bosnian Serb leader, Milorad Dodik, rigged the vote on Sunday to win the position that he sought.

Dodik, the most powerful Bosnian Serb politician since 2006, denied the allegations, including a claim by protesters that poll workers loyal to his political party, SNSD, had altered vote tallies to reduce the number of ballots cast for his contender, Jelena Trivic, and hand him the victory.

Bosnia’s election commission president, Suad Arnautovic, said Friday the body had to order the unsealing of ballot boxes and vote recounts at around 1,000 polling stations —16% of all such locations in the country. He said that's because poll workers there “did not do their job in accordance with the law.”

“They failed to fill out necessary forms…(and) some of their vote tallies were contrary to the rules of mathematics,” he said.

Ballots and other election material from the affected polling stations, spread over 60 different cities and municipalities, were being shipped to the central vote counting center in the capital of Sarajevo to be further examined, Arnautovic said.

Bosnia’s general election included races for different levels of government in one of the world’s most complicated institutional set-ups. Bosnia's political structure was agreed upon in a U.S.-sponsored peace deal that ended more than 3½ years of bloodshed in the 1990s between its three main ethnic groups: Muslim Bosniaks, Orthodox Serbs and Catholic Croats.

The peace agreement divided the country into two highly independent governing entities — Serb-run Republika Srpska and the other shared by Bosniaks and Croats. Each entity has its own president, parliament and government, but the two are linked by shared, multi-ethnic institutions.

The election on Sunday included contests for the three members of Bosnia’s shared, multi-ethnic presidency, parliament deputies at different levels of governance and the president of Republika Srpska, which Dodik was running for.

Under Bosnia’s electoral rules, votes are counted at polling stations by poll workers who are appointed by the country’s central election commission but are all nominated by political parties and coalitions that are running in an election. The central election commission collects poll station tallies, examines them for irregularities and runs recounts where necessary before certifying the results of a vote.

The commission has for years called for electoral law reforms, insisting that appointments of poll workers by political parties increases the risk of vote-rigging.

“I fear that many polling station committees will be the subject of criminal investigations,” said Irena Hadziabdic, a commission member.

However, she added: “Rest assured that (the central election commission) will not undermine our own integrity…we will do our best to investigate all complaints and irregularities.”