Tensions between Pristina and Belgrade have been heightened since a police officer was killed last month in an ambush in Kosovo’s restive north, allegedly by a paramilitary unit made up of Kosovo Serbs, according to France24.

“The major events on 24th of September exacerbated an already deteriorating security environment characterized by an atmosphere of mutual suspicion… touching much of the population, especially in northern Kosovo and among Kosovo-Serb communities,” Caroline Ziadeh, head of the UN’s mission Kosovo, told the UN Security Council.

Animosity between Kosovo and Serbia has persisted since a war between Serbian forces and ethnic Albanian insurgents in the late 1990s that drew NATO intervention against Belgrade.

Kosovo, which counts 120,000 Serbs among its 1.8 million people, declared its independence from Serbia in 2008, in a move Belgrade has never recognized.

But existing tensions have been heightened in Kosovo’s north for months.

Protests flared earlier this year among Kosovo’s ethnic Serbs in April after the authorities installed Pristina-allied mayors following widely boycotted local elections in four predominantly Serb northern municipalities.

“The current political impasse, with its impact on the security and well-being of the population, can only be overcome through compromise,” Ziadeh said.

“De-escalatory measures are critical to reduce tensions,” she said, adding she hoped that recent EU- and US-organized meetings with officials in Pristina and Belgrade would help “place the dialogue back on a forward path.”

Plans to establish an association of majority-Serb municipalities in Kosovo that would operate with some autonomy “should begin without delay or preconditions,” Ziadeh said.

Serbian Prime Minister Ana Brnabic meanwhile blamed Kosovo for the police killing, with Brnabic telling the Security Council last month’s unrest was “a logical consequence, unfortunately, of the reign of fear and terror that Pristina decided to enforce despite clear demands for de-escalation from the international community.”

Kosovo President Vjosa Osmani-Sadriu responded by accusing Belgrade of “ethnic cleansing through administrative means.”

Serbia is making “every possible effort to take our region back to the 90s,” she said.

“What happened on September 24 was not just an attack on Kosovo, it was a plan to destabilize the entire Western Balkans.”