Bosnia asked Switzerland on Monday to hand over the wartime Muslim defender of Srebrenica and not extradite him to Serbia, in a row that threatens to overshadow the 20th anniversary of the massacre.
Naser Oric, a hero to many Bosnian Muslims, was arrested by Swiss police last week on a warrant issued in 2014 by Serbia accusing him of war crimes against Bosnian Serbs in the Srebrenica region during the 1992-95 Bosnian war.
A Bosnian army commander at the time, Oric was in charge of organizing the defense of Srebrenica, a designated United Nations "safe area," from Bosnian Serb forces.
The town fell to the Bosnian Serbs in July 1995 and more than 8,000 Muslim men and boys were massacred in the days that followed. It was Europe's worst mass killing since World War II.
Serbia said on Sunday it had filed an extradition request.
Bosnia's state prosecutor's office, in a statement on Monday, said it had filed its own request for Oric to be returned to Bosnia, arguing that his extradition to Serbia would jeopardize a separate case against him in Bosnia.
Oric stood trial at a U.N. court in The Hague for crimes against Bosnian Serbs and was acquitted of all charges in 2008.
A spokesman for the Swiss justice ministry said the formal Serbian request arrived on Monday. Geneva prosecutors would question Oric about it and then the ministry would decide how to proceed based on this and any comments from his lawyer.
The Bosnian request had not yet arrived, he said.
A European accord spells out how to handle conflicting claims for extradition and Swiss authorities would have to consider all the circumstances, he said.
"If the request is based on the same crimes, then the place the crimes were committed plays an important role in deciding to which country to extradite," the Swiss spokesman said.
The possibility of Oric's extradition to Serbia has angered Muslim Bosniaks and may yet derail plans by Serbian Prime Minister Aleksandar Vucic to attend a ceremony to mark the 20th anniversary of the Srebrenica massacre in Bosnia on July 11.
"We appeal to Bosnian politicians to end diplomatic relations with Serbia and demonstrate that we will not stand silent while innocent people who defended this country get arrested," said Munira Subasic of the Mothers of Srebrenica association.