There is growing concern in Sarajevo over the arrival in the Serb-run half of Bosnia of a band of Russian cossacks, after it emerged that the group’s leader had commanded a cossack unit in Crimea.

According to Bosnian border authorities, 144 Russians have crossed into the country over the past week, and on Thursday some of them appeared in Banja Luka, the main town in Republika Srpska (RS – the Serb entity within the Bosnian state), dressed in traditional cossack costumes, complete with large black sheepskin hats. According to the Serb authorities, they had come to take part in a joint Russian-Serb commemoration of their alliance in the first world war. However, media reports in Sarajevo published photographs that appeared to show that the leader of the cossack troupe, Nikolai Djakonov, had led an armed cossack unit participating in the takeover of Crimea.

The arrival of the cossacks has come at a nervous time in Bosnian politics as the country approaches elections on 12 October. The RS leader, Milorad Dodik, has declared that if he wins he will declare the Serb territory’s independence from Bosnia, which would trigger an international crisis over the divided country, which fought a bloody war in 1992-95 costing the lives of 100,000 people. Russian volunteers, including self-styled cossacks, fought on the Serb side and were in Visegrad, on the river Drina, scene of mass killings of the local Muslim population, although there were no indictments issued against any of them by the subsequent war crimes tribunal in The Hague. One of the volunteers in Visegrad, a military intelligence officer known as Igor Girkin and Igor Strelkov, later became a leading figure in the separatist movement in eastern Ukraine. He has also taken part in re-enactments of first world war battles.

The first world war re-enactment in which Djakonov’s cossacks are due to participate is scheduled for 11 October, the day before the election, which Dodik is tipped to win.

However, few observers believe he will carry out his threat to declare Bosnian Serb independence, a threat he has made many times before.

“Dodik has no interest in an independent RS (if he truly believes in it). Serbia has no interest and will not support it, Russia is far away … and it would be an end to the RS as we know it,” Sead Numanovic, a veteran Sarajevo journalist, said. “The bottom line – even if there are a thousand cossacks, what is the point?”

Four days after the Bosnia vote, the Russian leader, Vladimir Putin, is expected in Belgrade, in next-door Serbia, where he will watch a military parade.