European Union Commission chief Jean-Claude Juncker on Friday warned of a new war in the Balkans if Bosnia, Albania, Serbia, Macedonia, Montenegro and Kosovo do not feel the EU is serious about offering them future membership.

“If, in Europe’s highly complicated landscape, the impression arises that we’re not serious about offering the prospect of EU membership to the western Balkans, then we might see later — and probably even sooner — what we saw in Balkans in the 1990s,” Juncker said in a speech to the Austrian parliament.