Serb protestors in Kosovo blocked roads for a second day on Sunday, following a nighttime exchange of fire with the police.
Kosovo's Serb minority is outraged by the arrest of a former Serb policeman suspected of involvement in attacks on Kosovo police.
Tensions in northern Kosovo, a hotbed of Serb nationalism, have mounted in recent weeks. Serbs have violently protested moves by authorities in Kosovo's capital, Pristina, which they deem anti-Serb.
A stun grenade was thrown at an armoured vehicle of EULEX, an EU mission tasked with patrolling northern Kosovo. No one was injured.
Josep Borrell, EU foreign policy chief, warned the bloc will not tolerate violence against members of its mission.
"Barricades must be removed immediately by groups of Kosovo Serbs. Calm must be restored," he tweeted on Sunday.
Hundreds of Serbs erected barricades on roads in the north of the country on Saturday, blocking traffic at two major border crossings with Serbia, police said. Both were closed on Sunday.
Trucks, ambulances and agricultural machinery were used to cut off traffic.
The latest protests were triggered by the arrest of a former police officer on Saturday.
He was one of two suspects wanted in connection with attacks on police patrols in recent days, according to authorities in Pristina.
Demonstrators told reporters they wanted to stop the arrested man from being transferred to Kosovo's capital.
Hostilities spiked after Pristina called for snap elections in four Serb-dominated communes in the north, organised for 18 December.
Shortly after the barricades were erected, Kosovo President Vjosa Osmani announced that she had decided to postpone local elections to April 23.
Serbs in the north reject Pristina's authority and Kosovo's
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