PRISTINA, Kosovo (News21USA) — Kosovo police raided several locations Friday in a tense Serb-dominated area in the country’s north, where weekend clashes left four people dead and further strained relations with Serbia.

Police said in a statement that they were conducting searches at five locations in three municipalities in northern Kosovo. A statement said the operation was related to Sunday’s shootout between Serbian insurgents and Kosovo police in the village of Banjska.

The standoff was one of the worst since Kosovo declared independence from Serbia in 2008 and Belgrade refused to recognize the division.

About 30 masked men opened fire on a police patrol near Banjska before breaking down the doors of a Serbian Orthodox monastery and barricading themselves inside with visiting priests and pilgrims. The gun battle that continued for 12 hours left one police officer and three gunmen dead.

The violence further raised tensions in the Balkan region at a time when European Union and United States officials have been pushing for a deal that would normalize ties between Serbia and Kosovo. A NATO bombing campaign against Serbian positions in Kosovo and Serbia led to the end of their 1998-99 war. The death toll was about 10,000 people, mostly Kosovar Albanians.

Serbian media said police raided a hospital and a restaurant in the Serb-dominated part of the city of Mitrovica on Friday, as well as locations in other towns in the area. Local news agency Kossev reported that police also confiscated several vehicles.

Kosovo has accused Serbia of direct involvement in the clashes in Banjska, which Belgrade has denied. Kosovo police said they had found huge quantities of weapons and equipment that suggested the insurgents were planning a broader operation.

On Thursday, Kosovo Interior Minister Xhelal Sveçla told The Associated Press in an interview that Serbia operates training camps for insurgents and that Kosovo authorities were also investigating Russia’s involvement in the violence.

There are fears in the West that Russia, acting through Serbia, wants to destabilize the Balkans and divert at least some attention from Moscow’s full-scale invasion of Ukraine. Russia has expressed support for Serbia over the fighting, blaming the West for allegedly failing to protect Kosovo Serbs.

The EU, with the backing of the United States, has been mediating negotiations between the two sides. In February, Kosovo Prime Minister Albin Kurti and Serbian President Aleksandar Vučić gave their approval to a 10-point EU plan to normalize relations, but the two leaders have since distanced themselves from the agreement.