Shortly before 7 AM three Croatian fishing boats, accompanied by Croatian police boats, entered Slovenian waters, Boštjan Šefic, a state secretary at the Slovenian interior Ministry, told reporters in Koper.

Slovenian police responded by warning the Croatian fishing boats that they illegally crossed the state border and were committing an offence, so proper procedures would follow.

The developments were documented, based on which the police will apply all necessary activities, Šefic said.

Another Croatian boat sailed into the Slovenian sea later, but Šefic said that it had been established this was due to a defect on the boat.

"Since then the situation in the Slovenian waters has been calm and now everything is running as per normal," the official said, adding that Slovenian authorities were controlling the entire Slovenian sea and had the situation "fully under control".

He regretted that offences and incidents, adding: "We'll do everything in our power to minimise and prevent that. In cases where necessary we will act in accordance with the law and issue fines."

The comments come as Slovenia started formally asserting sovereignty of land and sea it was awarded by the border arbitration tribunal half a year ago.

Šefic noted coordinated action by Slovenian authorities during the morning incident as the police were accompanied by a fishing inspector, who conducted his procedure and recorded the developments.

As the Croatian patrol boats attempted to prevent procedures, Slovenian police failed to fine the Croatian fishermen in the specific case. "Nevertheless, the police recorded the developments, identified the vessels and will continue suitable procedures later."

Šefic noted that the Slovenian police had been controlling Slovenian sea all the time and had responded to each entry by Croatian vessels: "What's new is that as of today we're issuing sanctions, that is conduct procedures against all of those who enter Slovenian waters illegally."

"Should the relevant Croatian authorities refuse to cooperate, we have other means at our disposal to serve those notices and enforce the fines."

Like elsewhere, police also have the discretion at sea to decide when to issue warnings instead of fines. "Police officers will decide accordingly. However, being that this is the state border, fines will definitely be issued more often."

With the implementation of the border arbitration award, Slovenian and Croatian fishermen can fish in the waters beyond the sea border, but Šefic noted that they needed to acquire permits.

The official reiterated that Slovenian police would protect Slovenian fishermen. "Except for Slovenian authorities, there can be no other state body in Slovenian waters and we'll act accordingly," he said, expressing the hope such measures would not be necessary.

Speaking about potential beefing of police units, the official said that certain activities had been taken "regarding matters of staffing, organisation and technical matters".

Deputy Police Commissioner Simon Velički emphasised that the Slovenian police force was operating in a non-conflict way.

He added that Slovenian police officers "are enforcing sovereignty over Slovenia's entire sea and will obviously be attentive to developments concerning our fishermen and if necessary provide them security".

According to Koper Police Department chief Danimir Rebec, the police have five patrol boats at their disposal, which enables them to have the situation at sea under control.

The newly determined border line at sea runs south of the median line in the Piran Bay after Slovenia was awarded 80% of the bay.

Croatia does not recognise the arbitration award and has instructed its fishermen to continue fishing halfway into the Piran Bay.