The former Yugoslav Republic of Serbia has become an official candidate for European Union (EU) membership, formally marking its democratic progress since the devastating wars of the 1990s.

The EU's decision was taken at a summit in Brussels late Thursday night, and launched the former pariah state on what will likely be a lengthy process towards full-blown membership in the Union.

After turning Serbia down in December, the latest move reflects growing fears among European leaders that a further rejection could undermine efforts to diffuse simmering ethnic tensions that remain in the Balkan region after its central role in orchestrating the collapse of Yugoslavia under the leadership of Slobodan Milosevic.

This is a remarkable achievement, European Council President Herman Van Rompuy told a news conference after the meeting, according to the Associated Press.

I hope it will encourage Serbia to make further efforts.

Serbia has had a tough time convincing European leaders of its suitability, with Romania nearly derailing its effort earlier in the week by refusing to sign a preliminary decision on the issue.

Bucharest demanded greater assurances over the protection of the rights of a Romanian minority in Serbia.

The Romanian protest, however, is seen by diplomats to be motivated more by the EU's reluctance to grant Romania access to the passport-free Schengen zone than fears for its ethnic minorities.

The EU is gradually dismantling the Balkans-shaped bomb lying right next to it, Daniel Korski, senior analyst at the London-based European Council on Foreign Relations told Reuters.

Over the next few months the EU's executive commission will review Serbia's strained relations with the break-away region of Kosovo, which it still does not formally recognize, and its efforts to tackle crime and corruption before deciding on when formal entry talks can begin.

But even if the go-ahead is given for formal entry talks in 2012, it may be years before the country becomes an EU member state.