There have been angry scenes outside the Austrian embassy in Sarajevo.
The crowd was outraged by the arrest in Vienna of Jovan Divjak.
The Serbian Army colonel defected to the Bosnian Army in 1992 at the start of the three-year war between the two countries.
He has been arrested on a warrant from Belgrade alleging war crimes.
“Divjak is a great man,” said one veteran of the conflict. “He chose his side and defended his honour as a soldier. He defended the state of Bosnia-Herzegovina and defended the people here. He fought to protect what the international community had left to fend for itself.”
Belgrade says Divjak’s role in an attack that killed dozens of predominantly ethnic Serb soldiers withdrawing from Sarajevo at the start of the war amounts to a war crime.
The case is particularly sensitive. The 73-year-old was the only Serb to be made general in the predominantly muslim Bosniak Army – fighting the ethnic Serbs who wanted to separate from Bosnia.