Delays to make Balkans part of the EU may act as a threat to security, according to Kosovo President Hashim Thaci.
Serbia is seeking a Russian air defense system in addition to fighter jets and battle tanks in what could fuel tensions in the Balkans.
A vote count of Serbia's presidential election confirmed that prime minister Vucic has won by a landslide in the first round of voting.
The prospect of EU membership has for years been the main driver of reform in the Balkans after a decade of war and upheaval in the 1990s.
The US Embassy in Croatia on Monday strongly denounced a march by far-right nationalists in the Croatian capital of Zagreb who also waved an American flag .