The gunmen fled to a nearby monastery where they barricaded themselves and traded gunfire with Kosovo police for hours, with at least three assailants shot dead.

Kosovo’s Prime Minister Albin Kurti said around 30 heavily armed gunmen were surrounded by authorities in the complex and called for their surrender.

Svecla said police had made several arrests during the clearance operation and seized a lot of weapons and equipment. However it remained unclear if all the gunmen had been apprehended during the sweep.

The attack and ensuing firefight marks one of the gravest escalations in Kosovo for years, following months of mounting tensions and stalling talks between the government in Pristina and Serbia.

The Serbian Orthodox Church also confirmed that gunmen had stormed the monastery in Banjska, where pilgrims from the northern Serbian city of Novi Sad were staying.

Pictures released by Kosovo authorities showed several heavily armed gunmen wearing uniforms, barricading themselves in at the monastery.

“We can see armed people in uniforms … they are firing on us and we are firing back,” Kosovo police official Veton Elshani told AFP by phone from Banjska.

Police later said in a statement that at least three attackers had been killed and one arrested during the firefight. Another four civilian suspects carrying radio equipment and weapons were also arrested.

Kosovo police also confirmed that the Jarinje and Brnjak border crossings between Serbia and Kosovo had been closed following the incident.

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Guns, grenades and rocket launchers surrendered after Serbia mass shootings

Guns, grenades and rocket launchers surrendered after Serbia mass shootings

Kurti’s comments at a press conference came hours after he called the ambush an act of terrorism and pinned the blame on the Serbian government.

“Organised crime with political, financial and logistical support from officials in Belgrade is attacking our country,” Kurti wrote on social media.

The NATO-led KFOR mission said its forces were present in the area, “standing ready to respond if required”.

According to Kosovo law, government authorities are not allowed to enter Orthodox properties, including churches and monasteries, without first receiving permission from the Serbian Orthodox Church.

Serbia’s President Aleksandar Vucic later condemned the killing of the police officer, but remained firm in putting the blame on Kurti for persecuting Kosovo’s ethnic Serbs.

Kurti “provokes all the time, I’m sorry that some of the Serbs fell for these provocations. Kurti is the only culprit, the only person who wants conflict and war,” Vucic told media.

The attack came more than a week after talks between the leaders of Serbia and Kosovo centred on improving ties failed to make a breakthrough during EU-mediated negotiations in Brussels.

The EU has been trying for years to resolve the long-running dispute between the Balkan neighbours that has soured relations since their war more than two decades ago.

Brussels believed it had broken the logjam by hammering out a plan to normalise ties in March, but since then there has been minimal progress.

The EU’s top diplomat Josep Borrell condemned Sunday’s attack, calling the targeting of police “hideous”.

“The responsible perpetrators must face justice,” Borrell wrote on social media.

Tensions in the troubled north have been smouldering for months, following the Pristina government’s decision to install ethnic Albanian mayors in four Serb-majority municipalities in May.

The move triggered one of the worst bouts of unrest in the north in years. Demonstrations followed, as well as the arrest of three Kosovar police officers by Serbia and a riot by Serb protesters in which more than 30 Nato peacekeepers were injured.

Kosovo remains overwhelmingly populated by ethnic Albanians, but in the northern stretches of the territory near the border with Serbia, ethnic Serbs remain the majority in several municipalities.

The clash in the north is just the latest in a long list of incidents to rock the area since Kosovo declared independence from Serbia in 2008. That was nearly a decade after Nato forces helped push Serbian troops from the former province during a bloody war that killed around 13,000 people.

Belgrade – along with key allies China and Russia – has refused to recognise Kosovo’s independence, effectively preventing it from having a seat at the United Nations.