US sanctions imposed on Milorad Dodik last week have underlined the shifting opinion about the Bosnian Serb leader in western capitals — and the resurgent threat of ethnic tension in the Balkans.

Dodik was first elected as Bosnian Serb leader more than two decades ago, in the wake of peace accords that ended Europe’s deadliest conflict since the second world war. He was viewed in the west as a figure capable of helping Bosnia — split between a Serb-controlled entity and another dominated by Croats and Bosniaks — move beyond its sectarianism.

But the increasingly nationalist politician has portrayed the 1995 Dayton peace accords as a vehicle of western interests. He has boycotted Bosnia’s institutions since July and wants to end Bosnian Serb co-operation on matters such as defence, tax and judicial affairs. The prospect of what in effect would be a quasi-secession has sparked international warnings of the risk of renewed ethnic violence.