Kosovo Albanians rejected a reworked offer of wide-ranging autonomy from Serbia on Tuesday and said there were no alternatives to the province's demands for outright independence.
Four hours of internationally mediated talks described by both sides as "intense and difficult" ended with mutual recriminations over who was to blame for the lack of compromise.
Mediators from the EU, Russia and the US are racing to try to narrow the gap between the sides before a Dec. 10 deadline for reporting back to the UN secretary-general. With Kosovo threatening to declare independence unilaterally if no deal is reached by then, there are fears about the possibility of a new wave of violence in the Balkans.
Serb and ethnic Albanian leaders will meet for a final round of talks over three days next week in Baden, Austria.
Serbian President Boris Tadic said his country would not be held to the de facto Dec. 10 deadline.
"We are not accepting artificial deadlines," he said.
A member of the ethnic Albanian negotiating team, Skender Hyseni, accused the Serbs of seeking "to drag this process until hell freezes."
The negotiations have plodded along for two years with little to point to in the way of progress.
The Serbs sought to present themselves as the more constructive party at Tuesday's talks in Brussels.
"Serbia has always been constructive ... always looking for compromise, if someone is wasting time, its not Serbia," Serbian Prime Minister Vojislav Kostunica said after the talks.
The Kosovo delegation said the Serbs' latest autonomy proposal did not go far enough.
"I'm afraid I cannot report any progress," Hyseni said. "That's mainly because of the lack of willingness ... on the part of the Serbian delegation to acknowledge the reality in Kosovo."
"Kosovo is not ready to wait so long," Hyseni said. Kosovo would act soon after the Dec. 10 deadline to declare independence, he said.
"Our vision and our stance is very clear: It's the independence of Kosovo and its recognition," Kosovo President Fatmir Sejdiu said. "There are absolutely no alternatives."
Belgrade has proposed before granting Kosovo a high degree of autonomy with which to run its own affairs. Kosovo's ethnic Albanians have rejected the suggestion.
It was unclear how the new Serb proposal might differ from earlier ones.
Serbia's Minister for Kosovo Slobodan Samardzic said it was based on the type of autonomy held by Finland's Aland islands, which control their own affairs, apart from security and foreign policy.
Kosovo officials said other models put on the table included US territory Puerto Rico and Hong Kong and Macau -- places which also have substantial autonomy but are not independent.
All sides have suggested the negotiations are unlikely to provide a compromise by Dec. 10.
The three envoys, led by the EU's representative at the talks, Wolfgang Ischinger, presented both sides with plans to develop practical partnerships in trade, policing and border issues without addressing independence.
Ischinger, along with the other two mediators -- US representative Frank Wisner and Russian diplomat Alexander Botsan-Kharchenko -- sat down with the Kosovo and Serbian leaders to discuss possible resolutions.
Kosovo has been under UN control since 1999, when NATO intervened to stop a Serbian military crackdown on ethnic Albanian separatists. NATO is in charge of Kosovo's security and keeps a 16,000-strong peacekeeping force in the province.