Tensions soared in the Balkans a day before Kosovo's parliament is set to approve the formation of an army, with Serbia warning Thursday that the move would threaten peace in the war-scarred region, ABC News reported quoting AP.

Kosovo's parliament is expected to pass legislation Friday that would turn an existing 4,000-strong security force into an expanded, lightly armed army. Kosovo declared independence in 2008 from Serbia, which does not recognize the assertion of statehood.

After talks with the head of the U.N. mission in Kosovo, Serbian President Aleksandar Vucic described Kosovo's decision as a "new provocative and one-sided measure" that raises Serbia's concerns for the future of Serbs in Kosovo.