Permanent Court of Arbitration

Day 414 of the invasion of Ukraine. Summary of key events in the last 24 hours:

Slovenia on Friday submitted to the European Commission a letter of complaint against neighbouring Croatia for its refusal to abide by an arbitration court ruling on a border dispute in the Adriatic Sea.

The dispute between Croatia and Slovenia over the Piran Gulf risks going up another notch after Croatian police offered to accompany Croatian fishermen in the waters of the Piran Gulf and ward off any Slovenian attempts to issue them with penalty notices.

The two former Yugoslav republics are locked in an unresolved dispute over the waters off the Istrian peninsula, which both claim.

Slovenian Foreign Minister Karl Erjavec said that Ljubljana was preparing to file a lawsuit in the EU court against Zagreb due to Croatia's non-compliance with the decision of the Permanent Court of Arbitration as for the borders between the two nations.

After months of rows and cancelled meetings, Slovenian Prime Minister Miro Cerar is visiting Zagreb on Tuesday to meet his Croatian counterpart Andrej Plenkovic in the hope of moving forwards towards a resolution of the territorial dispute between the two states.

Kosovo's government is considering taking the issue of border demarcation with Montenegro to the Permanent Court of Arbitration in The Hague, if Montenegro continues to refuse to review the agreement, which its parliament already ratified.

Slovenian Prime Minister Mirko Cerar on Thursday said that he was cancelling his visit to Zagreb after his Croatian counterpart, Andrej Plenkovic, told the UN in an address that Slovenia had "compromised" international arbitration of their dispute over the Piran Gulf.

Croatian Prime Minister Andrej Plenkovic and his Slovenian counterpart, Miro Cerar, meeting in New York for the UN General Assembly session, agreed to meet again in Zagreb on September 27 to discuss the dispute over the territorial waters between Croatia and Slovenia in the Piran Gulf.

Romania and Croatia face a veto from their neighbours, Hungary and Slovenia, on Friday in Paris, when the Organisation for Economic Co-operation and Development, OECD, discusses their applications for membership.

Hungary on Wednesday said it would block Romania's membership application over the closure of a Hungarian-language Catholic school in Transylvania.

More than a quarter of a century since the Yugoslav federation fell apart, the borders between most of the former constituent units - Bosnia, Croatia, Kosovo, Macedonia, Montenegro, Serbia and Slovenia -remain unresolved.