Western Balkan leaders and EU delegates are meeting in Slovenia to attempt to present a common front in the region's path towards EU membership, BBC reported.
But Serbian President Boris Tadic is boycotting the event because of the presence of Kosovo's prime minister.
Belgrade rejects the declaration of independence by Kosovo - Serbia's southern province - two years ago.
It is a major blow to the event and to the changed image that the region is now trying to present to Brussels.
The original aim of bringing all Western Balkan leaders together here in Slovenia was to show regional unity - that despite the conflicts of the 1990s and ongoing internal and bilateral problems, all countries are now determined to march forward together towards the goal of European Union membership.
The challenges each face are substantial.
Bosnia is in a state of political paralysis, with the different ethnic groups failing to agree on any meaningful reform.
Albania is still in its transitional phase from years of communist isolation to fully-functioning democracy.
Macedonia's progress is blocked by a dispute with Greece over its name.
But the most intractable problem of all is that of Kosovo - Serbia's southern province which declared independence two years ago, an act which Serbia refuses to recognise.
Despite last minute diplomatic negotiations, Serbian President Boris Tadic has decided to boycott the summit because Kosovo's Prime Minister Hashim Thaci is attending.
But the conference will go ahead anyway, with analysts believing that Serbia will begin to change tack once the International Court of Justice delivers its verdict later this year on the legality of Kosovo's independence - a symbolic opportunity to begin a new chapter in Serbia-Kosovo relations.
Many tough years of reform still lie ahead for the majority of these countries on their paths to the EU, but membership is seen as a way of pacifying a still fragile region and drawing a line under its turbulent past.
And for Slovenia - the host of this summit and the only EU member among them - it is a way of leading by example, of saying: "We managed to get there - now you should all follow suit."