"The Commission will continue to act as an honest broker to facilitate such a solution. With regards to the next steps of this process, our two member states concerned are the best place to continue talking and comment," the Commission spokesman Margaritis Schinas said answering a journalist question at a regular press briefing.

Article 259 does not create a legal obligation for a Commission report, he explained. So far the Commission has issued an opinion in four out of eight similar cases.

According to him, the Commission's position is known: the solution is to be found between the two member states and the Commission stands ready to help.

Croatia's newspaper Večernji List reported earlier today that the Commission's legal service had proposed to the Commission to back Slovenia in two of the four points listed in the letter on the lawsuit against Croatia over its non-implementation of the arbitration award.

Asked to comment on this, Schinas said he could not comment on the documents of the Commission's internal services.

He noted though that the college discussed the subject in July last year based on an oral presentation by the legal service, which "set the parameters for the Article 259 in which we still are in the sense that this arbitration procedure is still very much the only framework that we think can be helpful."

Asked whether the Commission could issue an opinion on the lawsuit after today's deadline, Schinas said that this was not a legal deadline nor a legal obligation. "There are two options. One option is a report, one option is without a report."

"I think the fact that this spirit of time expires today, clearly shows that the Commission will not issue a report."

While Croatia is insisting that it is not violating EU law by ignoring the arbitration award, Slovenia launched on 16 March proceedings on the basis of Article 259 of the Lisbon Treaty, which enables a member state to sue another member at the EU Court of Justice due to EU law violations.

The process was launched with a letter to the European Commission, reportedly including a concrete list of violations entailed in Croatia's refusal to respect the arbitration decision.

These include the violation of the principle of the rule of law, the undermining of Slovenia's ability to implement EU law and violations of Schengen rules and common fisheries rules.

Večernji list reported the Commission's legal service agreed with Slovenia when it comes to Schengen and fisheries.

Since the three-month period for the Commission to issue an opinion expired today, Slovenia can go ahead and file a lawsuit at the EU Court of Justice. It is not clear yet if or when Slovenia will do so.

Večernji List also reported today that European Commission President Jean-Claude Juncker had until recently intensively communicated with the Croatian and Slovenian prime ministers to find a solution and proposed the signing of a memorandum, presenting the arbitration award as a bilateral agreement.

The Slovenian government denied the report.