The fishermen, in one case escorted by the Croatian police, entered in the area of the bay controlled by the Slovenian police, leaving it after being warned of the fact.

According to Sunday's press release from the Slovenian police, a Croatian fishing vessel entered the area under Slovenian control on Saturday morning and started fishing.

The Slovenian police warned the crew that they were fishing in the Slovenian territorial waters, after which two Croatian police boats arrived at the scene.

After being informed by the Slovenian police crew that they had entered Slovenian waters, the Croatian police boats and the fishing boat left the area towards the Croatian town of Savudrija, the release says.

The second incident took place on Saturday afternoon, with a Croatian fishing boat escorted by Croatian police boats entering an area controlled by the Slovenian police.

The Croatian boats left for Savudrija after being warned that they were located in an area under the control of the Slovenian police.

The police failed to specify where exactly the incidents took place, saying that nothing had changed regarding the implementation of their tasks on the border.

The tasks "are being carried out in the same way as before the announcement of the ruling of the arbitration tribunal".

The Croatian Foreign Ministry meanwhile reported that Slovenian police boats had crossed the median line in the Bay of Piran three times on Saturday.

It said that the Croatian police officers warned their Slovenian colleagues in all three cases that they had entered the Croatian territorial waters, after which they had returned in the Slovenian waters.

Foreign Minister Karl Erjavec commented on the incidents for commercial broadcaster POP TV, saying that he regretted them taking place.

"I think that this shows that the Croatian side is very nervous," he said, announcing that a diplomatic note would be sent to Croatia on Monday afternoon.

"Croatia will be officially acquainted with this note on Tuesday," he added.

The foreign minister believes that Slovenia and Croatia should form a joint commission which will discuss helping Slovenians who were left on the Croatian side after arbitration and vice
versa.

The incidents took place after the arbitration tribunal awarded on Thursday more than three quarters of the bay to Slovenia and determined a 2.5 nautical mile wide junction between Slovenian waters and the high seas.

Croatia does not recognise the arbitration decision, having argued that the procedure had been "irreversible contaminated" after a wiretapping scandal in mid-2015 revealed contacts between the Slovenian arbitrator and agent.