Although Macedonia is the one of the four aspiring countries - along with Bosnia-Herzegovina, Georgia and Montenegro - which meets all the criteria, it still faces a name dispute with Greece, so the best prepared country is Montenegro, Erjavec explained.

Erjavec expects the foreign ministers will call at the ongoing session for a report on the four candidates' progress to be prepared by June, which could then serve for the discussion of members ahead of the summit.

He explained that a group of countries was already forming in support of enlargement to the Western Balkans. The group includes Hungary, Romania, Slovakia and Canada, while no NATO member has taken a position against enlargement, Erjavec noted.

Slovenia strongly supports NATO's open-doors policy, Erjavec stressed, adding that the candidates should not be treated in a package.

The ministerial is meanwhile focusing on advancing transatlantic ties and the alliance's future after 2014, also with respect to its role in Afghanistan. However, with the complications in the country, the debate on NATO's presence there remains open.

Even if the Resolute Support mission to Afghanistan is endorsed as a way of continuing the NATO presence after the ISAF mission concludes in 2014, the member states are expected to contribute only around a tenth of their current deployment, which in Slovenia's case means around ten soldiers.