The European Union on Monday warned of "escalation and violence" after emergency talks between Kosovo and Serbia failed to resolve their long-running dispute over car licence plates used by the ethnic Serb minority in Kosovo.
"After many hours of discussion ... the two parties did not agree to a solution today," EU foreign policy chief Josep Borrell said in a statement to the media.
"I think that there is an important responsibility on the sides of both leaders for the failure of the talks today and for any escalation and violence that might occur on the ground in the following days."
Borrell later discussed the matter with NATO Secretary-General Jens Stoltenberg, who said in a tweet that the NATO-led peacekeeping force in Kosovo was "vigilant".
"Now is the time for responsibility & pragmatic solutions. Escalation must be avoided," he said.
Late on Monday, KFOR Commander Angelo Michele Ristuccia appealed to all parties to avoid any actions that could exacerbate the situation.
A KFOR spokesperson said the major general had met with Kosovo's Interior Minister Xhelal Svecla and stressed the importance of avoiding escalation.
Around 3,700 NATO peacekeepers are still stationed in the former Serbian province to prevent violence between ethnic Albanians and Serbs.
Kosovo has attempted this year to require its Serb minority to change their old car plates that date before 1999 when Kosovo was still part of Serbia. Serbs in the northern part of the country have resisted, sometimes violently, but Kosovo has said it will start issuing fines from Tuesday.
Borrell said an EU proposal could have avoided increased tensions but while Serbian President Aleksandar Vucic accepted the proposal, Kosovo Prime Minister Albin Kurti did not.
Borrell said he would inform the EU member states of the two countries' "lack of respect for their international legal obligations" and warned that, given their commitment to joining the bloc, they should act accordingly.
"The Serbian side was completely constructive and we were accepting the texts that were changed 10 times, but the Albanian side did not want to accept anything, not for a second, they would always add something that was clearly not possible," Vucic told reporters after the meeting.
Kurti said he was ready to hold further meetings to normalise relations between Belgrade and Pristina, not just to deal with one issue.
"We cannot be irresponsible and not treat the actual issues ... We cannot turn ourselves into state leaders that are dealing only with car plates and are not talking how to normalize their relations," he told reporters in Brussels.
Speaking in Belgrade after the meeting in Brussels, Vucic said he would meet Kosovo Serbs late on Monday to ask them to remain calm.
"We received the latest intelligence a little while ago, the situation is very difficult and it is on the verge of conflict," Vucic told reporters. "We will do everything to preserve peace."
He also said Serbia would stop issuing and renewing its own car number plates for Northern Kosovo.
The dispute over licence plates has stoked tensions for almost two years between Serbia and its former breakaway province, which declared independence in 2008 and is home to a Serb minority in the north backed by Belgrade.
Around 50,000 ethnic Serbs who live there refuse to recognise Pristina's authority and still consider themselves a part of Serbia.
Hundreds of police officers, judges, prosecutors and other state workers from the Serb minority quit their jobs this month after the government in Pristina ruled that local Serbs must finally replace car plates issued by Northern Kosovo Serb municipal authorities loyal to Belgrade, with Kosovo state ones.
Borrell called on Kosovo to immediately suspend the re-registation of vehicles in north Kosovo, and asked Serbia to suspend issuing new number plates, allowing both parties "space and time" to find a resolution.
State Department spokesperson Ned Price said the United States joined the EU "in calling on Kosovo to immediately suspend any planned measures that would escalate tensions, including the imposition of vehicle fines" and that both sides should "refrain from taking provocative steps."
(Additional reporting by Bart Meijer, Philip Blenkinsop, Costas Pitas, Sabine Siebold and Fatos Bytyci in Pristina; Writing by John Chalmers; Editing by Josie Kao, William Maclean and David Gregorio)
