Bildt emphasized, however, that the EU has no obvious role to play in the dispute at the moment and that the two Balkan countries need to work together to resolve the matter.
The 18-year-old border dispute has blocked Croatia’s European Union membership talks since December, and Slovenia is demanding it be resolved before the accession negotiations resume.
“Now is the time for a period of reflection in both countries,” Bildt told reporters in Brussels, after a new round of talks between Zagreb and Ljubljana ended in acrimony Thursday.
“We will see if that reflection — at some point in time — has any results,” said Bildt, who helped negotiate during the war in Bosnia in the 1990s.
“If they have anything to say, I will be a very keen listener.”
The EU’s executive body, the European Commission, has been trying to broker an accord, and proposed in April to set up a tribunal to arbitrate.
The row involves a small piece of land and sea and dates back to 1991, when the two proclaimed independence from the former Yugoslavia. Slovenia joined the EU in 2004 and Croatia hopes to become the EU’s 28th member by 2011.
Officials said Thursday’s talks ended in a new stalemate after Croatian Prime Minister Ivo Sanader made two new proposals to the compromise being offered by the commission.
“This is a bilateral dispute. The responsibility for solving bilateral disputes rests with the countries,” Bildt said.
“They should not impede the accession negotiations in our opinion, but they have done so as we know.”
Slovenia has viewed EU mediation as a way to resolve the row, but Croatia considers it simply a stepping stone to a resolution before the International Court of Justice in The Hague.
A key point for Slovenia is securing free access to international shipping waters by getting a corridor that would cross Piran Bay, which is currently controlled by Croatia.
Sanader conceded Thursday that negotiations on Croatia’s entry to the European Union might not be concluded this year as hoped.