Both countries, which had sought arbitration to resolve their two-decade long border dispute, were notified of the anticipated timetable for the ruling in a written notification on Friday.

The notification states that the court "contemplates rendering the award in mid-December 2015". "Further information regarding the rendering of the award will be made available...in due course".

The announcement comes after weeks of speculation when the court could rule on the border after more than three years of arbitration proceedings.

Following the presentation of oral arguments in June 2014, the two countries said they expected a ruling in the first half of 2015.

But in recent weeks, media have speculated that the ruling could come in the autumn or even later, possibly after the Croatian general election expected to be held in early 2016.

The court is not bound by a deadline for issuing the ruling, with the arbitration agreement specifying it must render it "expeditiously after due consideration of all relevant facts".

The Slovenian Foreign Ministry confirmed it had been notified of the expected rendering of the ruling. It said that the court was free to decide on the date independently and that "Slovenia is satisfied with the [set date]".