"In light of that problem, there can be no further accession by Western Balkan countries [to the EU] without border disputes first being resolved," Juncker told the European Parliament in Strasbourg.
According to the politician, one can not assert that the problem will be resolved after accession.
"Responsibility needs to be shown by Croatia and Slovenia, the problem has to be resolved before the further accessions," Juncker stressed.
Slovenia obtained the right of access to international waters through Croatian territorial waters in the Adriatic Sea, as well as three-quarters of the Piran Bay area. Croatia does not accept this decision, as it previously withdrew from the arbitration agreement.
The two countries agreed to settle the dispute by arbitration in 2009, but in 2015 Zagreb said that the court had compromised itself by divulging classified information. According to Croatian Prime Minister Andrej Plenkovic, up to fifty Croatian fishermen in small vessels are engaged in traditional fishing in the disputed part of the Gulf of the Adriatic.
New EU strategy for the Western Balkans
Speaking about the new the new EU strategy for the Western Balkans later on the day, EU foreign policy chief Federica Mogherini explained that it stipulated the Balkan states' integration with the European Union, including the possibility of the accession of some of them by 2025.
"We will share a common future inside our European Union. This is the key political message that comes out of the strategy we just adopted in the College on Western Balkans strategy. A clear path for the Western Balkans — all our six partners in the Western Balkans to finally join the European Union," Mogherini said at a briefing.
The official noted that the year 2025 is not a deadline but a realistic perspective for the accession process, and expressed hope that other Balkan states would start accession talks in the upcoming months.
"There has been a lot of talks about the date, 2025 … It is clear for us that it is not a target date, this is not a deadline, this is a perspective, the text of the strategy is very clear. It is a realistic prospect to conclude the accession process for those that are currently negotiating, but also for others that might start negotiations in the near future," Mogherini said.
Of the Balkan countries, Albania, Macedonia, Serbia, and Montenegro are candidates for EU accession, and the negotiations are already in progress with Serbia (since 2014) and Montenegro (since 2012). Bosnia and Herzegovina have been waiting for a candidate status since February 2016.