Croatia's Foreign and European Affairs Minister Marija Pejčinović Burić said on Friday that Western Balkan countries had to resolve outstanding bilateral issues dating back to the 1990s war if they wanted to join the EU.
The fate of people gone missing in the war and the undetermined border on the Danube are among outstanding bilateral issues between Croatia, which joined the EU in 2013, and Serbia, which is negotiating accession.
"Southeast European countries must demonstrate the political will and clear commitment to reforms and fulfillment of EU membership criteria, which primarily concerns consequences of the war, reconciliation and outstanding bilateral issues," the ministry said quoting Pejčinović Burić.
Pejčinović Burić was attending an informal meeting of EU foreign ministers in Vienna, held as part of Austria's presidency of the EU.
They were joined by their counterparts from the candidate countries Albania, Montenegro, Macedonia, Serbia and Turkey.
The ministers confirmed their countries' commitment to EU membership prospects of all Southeast European countries, based on individual achievements and measurable progress, as well as on the implementation of reforms and respect for values as a precondition of further progress on their EU journey.
"Enlargement policy must continue to be based on strict and fair conditions and on the principle of individual achievements," said Pejcinovic Buric.
Several EU ministers expressed concern over a possible exchange of territory between Serbia and its former province of Kosovo, which has been announced as part of the efforts to improve relations between the two former enemies.
The EU has mediated talks between Belgrade and Pristina, offering them the prospect of EU membership if they resolved outstanding bilateral problems.
German Foreign Minister Heiko Maas expressed great scepticism about the plan, describing talks on territorial exchanges as unconstructive.
We believe that that could reopen old wounds in a broader sphere, said Maas.
Austrian Foreign Minister Karin Kneissl compared the situation with the abolishing of colonialism in Africa, when countries realised that discussions about borders would open a Pandora's box.
Any solution in the Balkans should primarily contribute to achieving regional stability, said European Neighbourhood Policy Commissioner Johannes Hahn.
Apart from the Western Balkans, the Vienna meeting's agenda also included the situation in the Middle East, transatlantic relations, migrations and the crisis in Venezuela.