The EU insists on regional cooperation because good relations between countries form a basis of the European community, Rehn said.
Addressing a regional meeting of the Stability Pact for Southeastern Europe in Belgrade, Rehn said that western Balkan countries would have a European prospect once they met the necessary criteria.
He said that he was satisfied with the assessment of international observers at the Montenegrin referendum on independence that the voting was carried out in line with international standards.
Opening the Belgrade meeting, Stability Pact Special Coordinator Erhard Busek said that the peaceful disassociation of Serbia and Montenegro was a sign of progress in the region.
Around 250 participants from 80 countries and organisations met today to discuss regional cooperation and the Pact's future role at the regular session of the Regional Table of the Stability Pact for Southeastern Europe.