A prominent Kosovo Serb politician, Oliver Ivanovic, was shot dead outside his party office in the Serb-run north of Mitrovica on Tuesday, reports BBC.
Ivanovic, seen as a moderate Kosovo Serb leader, was shot four times in the chest and died later in hospital, his lawyer Nebojsa Vlajic said.
Serbian government negotiators walked out of EU-mediated talks with Kosovo Albanians in Brussels after the news.
Kosovo remains ethnically divided since unilaterally splitting from Serbia.
Mitrovica - in northern Kosovo - is divided, with the south run by Kosovo Albanians.
Ivanovic, 64, headed a Kosovo Serb party called Freedom, Democracy, Justice. He had played a leading role in negotiations with Nato and the EU.
He was facing a retrial for alleged war crimes against ethnic Albanians committed in 1999.
In January 2016, EU judges in Kosovo sentenced him to nine years, but the verdict was overturned by an appeals court a year later. Ivanovic had denied all charges.
"This is a criminal and terrorist act that must be and will be punished," Serbian delegate Marko Djuric said, announcing his move to walk out of the Brussels talks.
Ivanovic rose to prominence in Kosovo Serb politics during the territory's conflict in 1999, when Serb forces battled Kosovo Liberation Army (KLA) guerrillas and committed war crimes against ethnic Albanian civilians.
Kosovo declared independence in 2008. It has been recognised by 115 countries, but not by Serbia and its ally, Russia.
