MITROVICA, Kosovo (AP) — A leading Serb politician in northern Kosovo was gunned down Tuesday morning, an attack that raised ethnic tensions in the Balkans and prompted the suspension of EU-mediated talks between Kosovo and Serbia.

Assailants opened fire on Oliver Ivanovic, 64, close to the offices of his political party in the Serb-controlled northern city of Mitrovica. He was taken to a hospital but doctors were unable to save him.

The doctors said Ivanovic had received at least five gunshot wounds to his upper torso. The assailants escaped in a car that was later found burned out. Kosovo police sealed off the area of the shooting and began a manhunt for the attackers.

Ivanovic was one of the key politicians in Serb-dominated northern Kosovo, a former Serbian province where tensions still remain high a decade after it declared independence in 2008. Serbia does not recognize that independence.

Ivanovic was considered a moderate who maintained relations with NATO and EU officials even after Serbia lost the control of its former province following NATO’s 1999 bombing to stop a deadly Serb crackdown against ethnic Albanian separatists.

A Kosovo court convicted Ivanovic of war crimes during the 1998-99 war. That verdict was overturned and a retrial was underway.

In Pristina, the Kosovo government strongly denounced the slaying, saying it considers the attack a challenge to “the rule of law and efforts to establish the rule of law in the whole of Kosovo territory.”

In Belgrade, Serbian President Aleksandar Vucic held a top security meeting to discuss the shooting. Afterward, he called the killing “a terrorist act” and said Serbia is demanding that international missions in Kosovo include Serbia in their investigation into the slaying.

“Serbia will take all necessary steps so the killer or killers are found,” he said.

At the news of Ivanovic’s slaying, the Serb delegation at the EU talks in Brussels immediately left to return to Belgrade.

Delegation leader Marko Djuric said “whoever is behind this attack … whether they are Serb, Albanian or any other criminals, they must be punished.”

European Union foreign policy chief Federica Mogherini called the presidents of Serbia and Kosovo to express the EU’s condemnation of the killing. She appealed for both sides “to show calm and restraint.”

The head of the OSCE Mission in Kosovo, Ambassador Jan Braathu, said he was “shocked and deeply saddened” and considered Ivanovic “among the most prominent Kosovo Serb representatives for almost two decades. ”

He also urged “all sides to avoid dangerous rhetoric and remain calm at this sensitive time, and recommit themselves to continue the work toward the normalization of relations and improvement of the lives of the citizens of Kosovo and Serbia.”