In a resurgence of violence in Kosovo’s restive north, gunmen in armored vehicles stormed a village in the Serb-majority region on Sunday, clashing with police and barricading themselves in a monastery, clashes that left four dead, News.ro reported, citing Reuters.

Kosovo police said one officer and three of the approximately 30 attackers were killed in a shootout near the village of Banska.

Monks and pilgrims were locked inside the Serbian Orthodox monastery’s place of worship and the siege lasted for hours.

Ethnic Albanians make up the vast majority of the 1.8 million inhabitants of Kosovo, a former province of Serbia. But some 50,000 Serbs make up the majority in the north, where clashes with the authorities have been ongoing since May, injuring dozens of protesters, including NATO peacekeepers.

Serbs have never accepted Kosovo’s 2008 declaration of independence and still claim Belgrade as their capital, more than two decades after a guerrilla uprising by ethnic Kosovo Albanians against the repressive Serbian regime.

“They are professionals”

It is unclear who is behind Sunday’s violence, but Kosovo Prime Minister Albin Kurti and Interior Minister Jelal Svekla blamed “Serbian-sponsored criminals”.

“They are professionals, military and police trained,” said Kurti, who urged them to surrender.

Serbian officials had no comment, but President Aleksandar Vucic was due to make a statement later in the evening.

The Diocese of the Serbian Orthodox Church in Raška-Prizren, which includes Banska, said that men in an armored car broke into the monastery premises, forcing visiting monks and believers to barricade themselves in the place of worship. “Armed men in masks are moving around the yard, shots can be heard from time to time,” the diocese reported. “The diocese strongly condemns the open violence practiced in the premises of the Serbian Orthodox Church, calling on all parties to end the conflict as soon as possible,” the statement said.

The police said that the attackers first parked heavy vehicles on the bridge at the entrance to the village. They shot at police officers who approached them before heading to a nearby monastery.

In addition to the four dead, three policemen were injured during the shootout, the Kosovo police reported.

International condemnation

The head of the UN mission in Kosovo, Caroline Ziade, and EU foreign policy chief Josep Borrell condemned the violence.

“Several innocent lives are at risk in the ongoing fighting around the Banska monastery,” Borrell said, adding that the EU and NATO missions in Kosovo are in contact with the authorities. “These attacks must stop immediately,” demanded the head of EU foreign policy.

According to a Reuters reporter nearby, NATO troops, along with EU police forces, EULEX and Kosovo police, were patrolling the road leading to Banska.

Journalists were not allowed into the village.

Local media reported that Kosovo’s border police closed two checkpoints with Serbia.

What do Serbs want in Kosovo?

Serbs in northern Kosovo have long demanded the implementation of an agreement reached by the European Union in 2013 to create a community of autonomous municipalities on their territory. EU-brokered talks on normalizing relations between Serbia and Kosovo stalled last week as the bloc accused Prime Minister Kurti of failing to create the association the Serbs had been demanding.

Prishtina sees the plan as a recipe for a mini-state in Kosovo, effectively dividing the country along ethnic lines.

Serbia still officially considers Kosovo to be part of its territory, but has denied suggestions that this would cause conflict within its neighbour’s borders. Belgrade accuses Pristina of violating the rights of the Serbian minority.

The unrest intensified when ethnic Albanian mayors took office in northern Kosovo after elections in April, despite being boycotted by Serbs.

NATO still has 3,700 peacekeepers in Kosovo, down from an initial force of 50,000 deployed in 1999.

The territory of northern Kosovo, populated by Serbs, is to some extent a de facto extension of Serbia. Local administration and civil servants, teachers, doctors and major infrastructure projects are paid for by Belgrade.