The initial results leaked by the Organisation for Security and Co-operation in Europe (OSCE), which ran the poll, suggested that Biljana Plavsic has lost the race to remain president of Republika Srpska to Nikola Poplasen, of the Radical Party.
The secretary general of Mr Poplasen's party, Ognjen Tadic, accused OSCE on Wednesday of delaying the release of the official results because its strategy had collapsed.
"The election process had been a disgrace," he said. "The OSCE has had an unprofessional attitude."
The organisation was expected to announce the results of the election earlier this week but cancelled the announcement abruptly and said the result would be released in 10 days.
Local journalists have also condemned the running of the election and its allegedly chaotic administration, which has cost pounds 20m and involved tens of thousands of local and foreign observers.
Since the 1995 Dayton peace accord ended Bosnia's vicious ethnic war, diplomatic efforts to ease out supporters of the UN-indicted war criminal Radovan Karadzic have centred on Mrs Plavsic.
Voters were left in no doubt that the West wanted Mrs Plavsic, a former hardliner who moved into the peace camp, to be re-elected and to reappoint her pro-Western prime minister, Milorad Dodic.
That strategy has now failed and the same hardline nationalists who started Bosnia's civil war in 1992 have triumphed in a free election, run by a Western body.
One worry is that if the half of Bosnia run by the Serbs is controlled by an ultra-nationalist, a fragile peace that has held since 1995 between the Bosnian Serbs and the Muslim-Croat Federation may collapse, resurrecting the danger of a second war.
The West has looked to Mrs Plavsic also to deliver on other items of the Dayton peace agreement. Those include the return of "ethnically cleansed" refugees to their homes in both halves of Bosnia and the handing over of all indicted war criminals, Mr Karadzic included, to the UN War Crimes Tribunal in The Hague.
Under Mrs Plavsic's administration, a few thousand Muslim refugees did return to Banja Luka and some other Bosnian Serb towns. That process will now be halted, and go into reverse, if Mrs Plavsic leaves office. Equally, the chances of Mr Poplasen and his allies handing over indicted war criminals to The Hague would seem to be nil.Reuse content