While Serbian President Aleksandar Vucic agreed to a proposal at an emergency meeting aimed at resolving a dispute over government-issued documents, Kosovo Prime Minister Albin Kurti refused, according to Josep Borrell, the EU’s top diplomat.

“Both bear full responsibility for the failure of the talks today and for any escalation and violence that might occur on the ground,” Borrell said on Monday.

The failure to defuse tension underscores persistent animosity between the two sides.  Kosovo broke away from Serbia following a war in 1998-1999 and declared independence in 2008.

The EU has been encouraging the countries to normalise ties – saying it will be a requirement to join the world’s largest trading bloc – but years of talks have yielded few results.

The dispute centres around a demand from Kosovo that ethnic Serbs in the Albanian-majority nation replace their identity documents and licence plates issued by Belgrade with new versions from Pristina.

Serbia also rejected part of the proposal, Jeton Zulfaj, an adviser to Kosovo’s premier, said on Twitter late Monday.

The change in documents would in effect recognise Pristina as the rightful government of Kosovo – a premise rejected by Vucic, a majority of Serbs, and ethnic Serbs living in Kosovo who remain loyal to Belgrade. Kosovo has repeatedly postponed a deadline for compliance, which is now set to expire at midnight on Monday.

In October, Kosovo Serbs threatened to set up blockades if the government in Pristina pushes ahead with the controversial plan. And earlier this month, hundreds of Serbs in northern Kosovo quit their jobs as police officers, judges and other positions in state institutions in protest.

The EU proposal centred around Kosovo not punishing ethnic Serbs who haven’t switched licence plates, and an agreement by Serbia to stop issuing them for places inside Kosovo.

Even though it wasn’t accepted, Borrell said that he now expected Kosovo and Serbia to immediately implement the points of the proposal.

He also said he would inform EU member states about both countries’ behaviour in the talks “and the lack of respect for legal obligations”, noting that would particularly apply to Kosovo.

Borrell also said that the resignations of about 600 ethnic-Serb police in Kosovo meant that there were fewer than 50 law enforcement personnel working in northern Kosovo.

“This leaves a very dangerous security vacuum,” he said. “The EU and our international partners have repeatedly called for de-escalation to no avail.”

(With assistance from Katharina Rosskopf and Natalia Drozdiak.)