"The only alternative is the full membership of these countries in the EU," Mr. Lajcak said on Saturday at the Balkan Integration Forum being held in Podgorica.
The European Union, he added, must be sure that new members do not bring additional problems to the bloc.
"What I fear is that we may lose the Western Balkans, which is committed to our values," said Mr Lajcak, adding that in the absence of alternatives, instead of creating states governed by the rule of law, independent media, civil society and depoliticized judiciary, there is a risk of strengthening illiberal authoritarian tendencies.
Such a Balkans, warns Mr. Lajcak, would be an instrument of change for the strategic interests of other players.