Borrell had mediated in the talks between Serbian President Aleksandar Vučić and Kosovo Prime Minister Albin Kurti, together with the European Union's Balkan special envoy Miroslav Lajčák.

Kosovo, which today is almost exclusively inhabited by ethnic Albanians, seceded from Serbia in 1999 with NATO support and declared itself independent in 2008, although it remains unrecognized by Serbia.

The planned agreement envisages that Belgrade will not recognize Kosovo under international law, but will take note of the statehood of its former province.

In particular, Serbia should recognize Kosovo's passports, licence plates and customs documents, which it has not done to date. Kosovo, in turn, will be bound to institutionally secure the rights of ethnic Serbs in the country.

At a first meeting in Brussels on Feb. 27, both sides had verbally agreed in principle to a draft agreement presented by the EU, based on a Franco-German proposal backed also by the United States.

Saturday's negotiations were to focus on concrete deadlines and dates to implement the individual points of the agreement.

As in Brussels, Vučić was reluctant once again to sign the agreement reached.

The deal was considered as accepted, Borrell said after Saturday's talks, while conceding that the two sides had not followed the more ambitious ideas presented by the EU mediators. He did not elaborate on the substantive differences.

Both sides would continue to work until they reached a substantive agreement, Borrell said.

"I have not signed anything today," Vučić told journalists in Ohrid. "We have each indicated in different ways where the respective red lines are for us." He described the atmosphere of the talks as "constructive."