Slovenia had built its lawsuit around the argument that Croatia infringes several articles of EU law by refusing to implement the award of a border arbitration tribunal that both countries had pledged would be binding. It claimed reference to the arbitration procedure in Croatia's EU accession agreement in effect made the arbitration agreement a part of EU law.

The court disagreed. While it is true Croatia's accession agreement EU makes a reference to the arbitration award, the judges did not see that as making the arbitration award a part of EU law. The reference to arbitration "could not be interpreted as incorporating into EU law the international commitments made by both member states within the framework of the arbitration agreement," the court held.

The decision is not surprising since the court's advocate general had used the same argument in delivering his opinion last year, arguing that "the infringements of EU law of which Slovenia accuses Croatia are ancillary to the issue of determining the boundary between those two states, which is a matter of public international law".

Despite the inadmissibility decision, however, the court indicated that both sides needed to respect the arbitration agreement. It said they were required by the EU Treaty to "strive sincerely to bring about a definitive legal solution to the dispute consistent with international law, in order to ensure the effective and unhindered application of EU law in the areas concerned".

It is this portion of the court's statement that Slovenian officials have invoked in claiming that the decision, which effectively means that EU legal avenues have been exhausted, is not a victory for Croatia as Croatian officials have interpreted it. In fact, they say it is a vindication of the Slovenian position.

Foreign Minister Miro Cerar said the ruling showed the court saw the border arbitration award as "valid and binding". The decision is "not a legal victory for Croatia," which will be "reminded every week that it must respect the arbitration award."

The court said the border between Slovenia and Croatia is determined with the arbitration award, "yet another proof that Slovenia has been right all along - that Croatia must implement the arbitration award as well," said Cerar. "No antics by the Croatian side can change this fact."

President Borut Pahor likewise stressed that the court decision did not change anything and Prime Minister Marjan Šarec said it was "not exactly time for our neighbours to pop open champagne" since Croatia will have to realise eventually that the arbitration award is valid and needed to be respected.

Slovenian specialists in international law said they were not surprised, but they pointed out that Slovenia had not lost anything in legal terms and the decision will have no bearing on implementation of the actual award handed down by the arbitration tribunal.

"Croatia is the legal winner, but the court has also stressed that legal agreements must be respected, and it indirectly said that the arbitration award is valid, which is what Slovenia has always claimed," said Verica Trstenjak, a former advocate general at the EU Court of Justice.

Janja Hojnik, a professor of EU law at the Maribor Faculty of Law, similarly labelled the decision as expected and said the court's appeal that the two countries must endeavour to resolve their dispute was "the most we could get".

With Croatia continuing to insist that the arbitration procedure has been compromised beyond repair by the Slovenian side as disclosed in a wiretapping scandal, the path ahead seems to be clear judging by the statements of senior officials: Slovenia insisting that the arbitration award must be implemented under international law.

This was also the message delivered by representatives of parliamentary parties. Most were critical of the court's decision, but the majority said efforts to implement the arbitration award needed to continue.

The other option would be to return to bilateral talks, which is what Croatia wants and which was the message senior Croatian officials delivered today. The court's decision is "a strong message to Slovenia that nothing can be achieved with unilateral measures, it takes an agreement with Croatia to find a solution for the shared border," Prime Minister Andrej Plenković said.

However, in Slovenia, the Democrats (SDS) are the only party to have seriously supported this option. While the SDS has been in opposition since 2013, the party has a shot at returning to power after the Šarec government collapsed this week.

Jurists consider this one of the options as well. Trstenjak said that while Slovenia will now have to insist on the implementation of the arbitration award, the two sides may also decide to ignore the award and engage in bilateral talks.

Marko Pavliha, a specialist in international law, said he saw no other way but for Croatia and Slovenia to return to the negotiating table. If that were to happen, however, Slovenia would be short-changed once again, he said.