Joachim Ruecker said on his return from Brussels that he had warned the European Union of the dangers of further delaying a decision the people of Kosovo had been led to expect by last October, after nearly eight years under UN rule.

Envoys of the Contact Group - the United States, Britain, Germany, France, Italy and Russia - resolved at a meeting in Vienna late on Wednesday to set up a new round of Kosovo talks, but failed to agree on a deadline for the negotiations.

A diplomatic source said Russia and the US agreed to a German proposal under which a "troika" of a single EU envoy, Russia and the US would oversee a new round of shuttle diplomacy between Belgrade and Pristina.

Serbia and Kosovo's ethnic Albanian leaders talked for 13 months under UN envoy Martti Ahtisaari with no compromise, and there is still no glimmer of a way out of that deadlock.

The United States, which backs Ahtisaari's plan for handing the ethnic Albanian majority a form of independence while seeking to protect its Serb minorities, warned on Wednesday that violence could return to the region if diplomacy failed.