Discussions mediated by the European Union to de-escalate tensions between Serbia and Kosovo ended without progress, bloc's foreign policy chief Josep Borrell said Thursday.

"We cannot sit and wait for the next crisis," said Borrell, deploring the lack of commitment by both sites to normalize their relations.

Kosovar Prime Minister Albin Kurti did not accept a proposal on how to move forward, although Serbian President Aleksandar Vučić would have supported it, said Borrell after hours of negotiations.

Under the proposal, Kurti was to start setting up an association of Serb-majority municipalities in Kosovo, while Vučić was to take steps toward recognizing Kosovo's independence.

Kurti however insisted on a de-facto recognition as a first step, Borrell said.

Kosovo, which is majority Albanian, was part of Serbia but unilaterally declared independence in 2008, after the two ethnic groups had been at war in the 1990s.

Tensions between the two sides have been running particularly high in recent months.

NATO peacekeeping troops in Kosovo came under attack in the north in May, with dozens injured on both sides in the clashes that erupted over the appointment of Albanian mayors in the region. The Serbian population had previously boycotted the elections on instructions from Belgrade.

Borrell regretted that Kosovo has not yet paved the way for new mayoral elections.

The EU's foreign affairs chief urged both leaders to recall their countries' ambitions to join the bloc.

"I think it's now finally time to take the process forward and to show that Kosovo and Serbia can live together in peace and be part of the European family," he said.