Kosovo’s prime minister on Sunday said one police officer was killed and another wounded in an attack he blamed on support from neighboring Serbia, increasing tensions between the two former war foes at a delicate moment in their European Union-facilitated dialogue to normalize ties.

Prime Minister Albin Kurti said "masked professionals armed with heavy weapons" opened fire on a police patrol in the village of Banjska, in Leposavic municipality, 55 kilometers (35 miles) north of the capital Pristina at 3 a.m. (1 a.m. GMT).

Kosovo police said two trucks without license plates blocked a bridge at the entrance to the village. Three police units were sent to unblock it but came under fire from different positions with various weapons, including hand grenades and bombs.

Police managed to push back the attack and take two injured police officers at the hospital in southern Mitrovica.

One of them was dead on arrival, doctors said. The condition of the other is not life-threatening.

Speaking after a meeting of the country’s Security Council Sunday, Kurti said it was a "sad day" for Kosovo and named the dead police officer as Afrim Bunjaku.

The prime minister displayed a set of photos which showed a number of four-wheel drive vehicles without license plates and an armored personnel carrier "which does not belong to the Kosovo police," near the Orthodox monastery in Banjska.

There was ongoing gunfire from what he described as a group of at least 30 military professionals, masked and heavily armed.

"It is clear that these uniformed persons, at least 30, are an organized professional unit who have come to fight in Kosovo," he said, calling on them to hand themselves over to the Kosovar authorities.

Most of Kosovo's ethnic Serb minority lives in four municipalities around Mitrovica, in the north.

Reports in Kosovo Serb media said residents of Banjska were woken by shootings and explosions in the night.

"It was a real little war: first some gunfire, then silence, shootings, detonations," Serbian Kossev news agency quoted an unidentified resident as saying.

Serbian media said both local roads and crossings with Serbia were blocked.

"Organized crime, which is politically, financially and logistically supported from Belgrade, is attacking our state," Kurti wrote on his Facebook page.

Kosovar President Vjosa Osmani, who is in New York at the United Nations General Assembly, denounced the killing.

"Such attacks testify once again to the destabilizing power of the criminal bands organized from Serbia which for a long time ... are destabilizing Kosovo and the region," she said.

In a statement, the U.S. ambassador in Pristina "strongly condemns the orchestrated, violent attacks on the Kosovo Police this morning," adding that "the Kosovo Police has full and legitimate responsibility for enforcing the rule of law according to the constitution and laws of Kosovo."

Serbia’s parliamentary speaker Vladimir Orlic said Kurti "was quick to blame the Serbs," adding that Kurti was the one who wanted an "escalation."

"He (Kurti) said it was some kind of organized action by professionals," Orlic told local Prva television station. "They must have been identified and he knows who they are and what they are, and everything is clear."

Earlier this month, an EU-facilitated dialogue meeting in Brussels between Kurti and Serbian President Aleksandar Vucic ended in acrimony. Washington has fully supported the negotiations and the stance of the EU.