A former Bosnian army general has been arrested in Austria and faces extradition to Serbia on war crimes charges.
Serbia says Jovan Divjak was involved in an attack that killed dozens of mainly Serbian soldiers leaving the Bosnian capital Sarajevo in 1992.
Gen Divjak was a Serbian colonel who defected at the start of the conflict in the former Yugoslavia.
He is expected to appeal against the extradition request, officials said.
Gen Divjak was taken into custody by Austrian police at Vienna airport following a flight from Sarajevo.
"There was a Serbian arrest warrant, the accusation is for participating in war crimes," Austrian interior ministry spokesman Rudolf Gollia told AFP news agency.
He could be held for several weeks while Austria obtains and examines documents supporting Serbia's extradition request, officials said.
Bosnian Foreign Minister Sven Alkalaj said the country's ambassador had been sent to offer Gen Divjak assistance.
Correspondents say the case is particularly sensitive.
In the Bosnian capital on Friday, several hundred people gathered in front of the Austrian Embassy to protest against the arrest.
But nationalist Bosnian Serb leader Milorad Dodik welcomed the move, saying: "He participated in and commanded war crimes."
Bosnia has always maintained that it acted in self-defence throughout the war and that Serbia was the aggressor.
Last year, Bosnia's wartime vice-president Ejup Ganic was arrested in London on a Serbian warrant relating to the same incident in 1992.
But a London court blocked his extradition, saying there was evidence that his trial could be "politically motivated".
The BBC's Mark Lowen in Belgrade says the legacy of the 1990s conflict weighs heavily on regional relations and prevents the former foes from moving on.