While Cerar stressed the importance of respect for international treaties, decisions of international courts and international law in his address to the assembly, Plenković said that international treaties and arbitration processes were only legitimate if they are conducted in line with rules.

"Compromising the impartiality or independence of international adjudicators and tribunals as was the case in the terminated arbitration process between Croatia and Slovenia make their decision legally void," Plenković said.

He said Croatia had had no other choice but to withdraw from the arbitration process. "We consider that this example of undermining the rule of law is a discouragement for states considering third-party discourse settlement."

Cerar told the press in New York that he had decided to cancel the meeting because of these statements.

He said that he and Plenković had agreed two days ago for the meeting to be held in Zagreb next Wednesday and to also discuss the border arbitration.

By making these comments "in front of all the countries of the world", "at the utmost formal level", Plenković withdrew from that agreement, Cerar said.

Saying that the arbitration is legally void is completely unacceptable for Slovenia and leaves no room for the talks in Zagreb, which is why the meeting no longer makes sense, Cerar said.

The Slovenian prime minister reiterated that the arbitration ruling was valid, noting that five independent international experts had decided that the decision was valid despite the "mistake that occurred".

He referred to the communication between the Slovenian arbitrator and the country's agent that was leaked by Croatian media in 2015, which Croatia used as argument to unilaterally withdraw from the arbitration process.

Cerar pointed out that Slovenia was open for dialogue, "but only when and if Croatia accepts the arbitration decision, so we can discuss its implementation".

According to the prime minister, Slovenia will in the coming days continue with its efforts to prepare for the implementation of the ruling. After the transitional period expires, Slovenia "will of course proceed with the implementation".

Elaborating on this, Pahor told the public broadcaster RTV Slovenija this meant that the necessary legislative changes would be drawn up, the ministries and "all other stakeholders" prepared for "appropriate actions that will be necessary for the implementation".

He said Slovenia still hoped that Croatia would cooperate in this process.