According to the Foreign Ministry, the secretary of state did not explicitly mention the arbitration agreement nor the importance of respecting the arbitration award.

According to a report by news portal Siol.net, this is a disappointment for Ljubljana, as the US is apparently leaning towards the Croatian side or at least "used the rhetoric which is significantly like the rhetoric of the Croatian diplomacy".

Tillerson said in the letter that the US would back any solution for determining the border at sea and on land that Slovenia and Croatia would adopt in consent.

He added that the US would not take any side in the conflict as both countries are its allies in NATO. He also called on both countries to work together and to find a solution. "The US are confident that both countries can achieve it," the Foreign Ministry quoted the letter.

In addition, the secretary of state expressed expectation that Slovenia and Croatia would abstain from provocative acts and confrontations, including in the Bay of Piran, because this does not only affect Slovenian-Croatian relations but also the stability of the region.

The Foreign Ministry said that Tillerson's letter was considered a response to a letter Erjavec wrote to the US in early July, immediately after the arbitration award had been announced. In the letter, Erjavec highlighted the importance of the arbitration award.

The ministry will continue to "explain Slovenian positions to the American side at all levels", as the importance of respecting the arbitration ruling is as important for the stability of the region as absence of any incident.

"Minister Erjavec will discuss the importance of respecting international law and decision of international courts with Secretary of State Tillerson at the first suitable opportunity for a bilateral meeting," the ministry added.

Siol.net also noted that the letter from the secretary of state came soon after Prime Minister Miro Cerar cancelled a planned visit to Zagreb after his Croatian counterpart Andrej Plenković again rejected the arbitration award at the UN General Assembly.

The portal added that the letter might have convinced Cerar to write to Plenković to continue talks.