Gunmen holed up in a northern Kosovo monastery clashed with authorities Sunday, according to Prime Minister Albin Kurti, hours after a police officer was killed when a patrol was hit by an ambush involving firearms and explosives.

Kurti said that the group of at least 30 heavily armed gunmen were now surrounded by authorities near the village of Banjska, where the patrol had been ambushed earlier Sunday, and called for their surrender.

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

"There are at least 30 professional, military or police armed people who are surrounded by our police forces and whom I invite to surrender to our security agencies," said Kurti during a press conference.

The Serbian Orthodox Church confirmed that gunmen had stormed a 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 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. 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.