The presidents of Serbia and Kosovo have abruptly called off a face-to-face meeting, dashing hopes of improved relations and a deal involving a land swap that could allow the Balkan neighbours to move towards European Union membership.
Kosovo's President Hashim Thaci was due to discuss the swap plan in Brussels with his Serbian counterpart, Aleksandar Vucic, for the first time in talks brokered by the EU's top diplomat Federica Mogherini.
But both men refused to speak to each other moments before their meeting was due to start at the EU's headquarters, diplomats said, leaving Mogherini to meet them separately several times during the day to keep talks alive.
It was not immediately clear what caused the breakdown.
"It went wrong today, they did not meet, they indulged in some drama instead," one EU diplomat briefed on the talks told Reuters news agency.
Mogherini said in a statement that "difficulties remain", adding, however, that she would seek another meeting with the two presidents later this month.
Vucic had planned to visit Kosovo this weekend and hold a rally, but a Serbian government official said he had now cancelled the visit. Vucic's office still has not issued a statement saying if the visit is cancelled.
The proposed land swap between the two countries would likely see a part of southern Serbia centred on the ethnic Albanian-dominated city of Presevo transferred to Kosovo, while the Serb-dominated northern part of Kosovo, around Mitrovica, would become part of Serbia.
The dispute between Serbia and Kosovo dates back to 1998-1999, when Slobodan Milosevic, a former Serbian president, ordered a bloody crackdown on Kosovo Albanian separatists. More than 10,000 people died in the conflict before NATO forced Serbia to pull out of the territory.
Kosovo, which declared independence in 2008, is recognised by more than 100 countries but not by Serbia, Russia and five EU countries - Cyprus, Greece, Romania, Slovakia and Spain.
Some fear that any border changes might trigger similar demands elsewhere in the Balkans, especially in Bosnia, Macedonia and Montenegro, which like Serbia and Kosovo, were part of the former Yugoslavia.
Serbia and Kosovo have been told to sort out their differences if they ever hope to join the EU. Officials from both sides have suggested a land swap could work, but the idea has been criticised both locally and internationally.
Germany warned in August that land swaps could enflame ethnic tensions in the region. But both the EU and the United States have said they would abide by an agreement, provided it respected international law.
Zoran Ostojic, an analyst from Belgrade, told The Associated Press he believed that Vucic and Thaci are "testing the ground, primarily with the international community" by floating the swap idea.
"Who knows where that could end?" Ostojic said, echoing fears of a chain reaction throughout Balkans.
Further high-level talks are scheduled to be held in Brussels later this month.