The Slovenian Ministry for Environment and Spatial Planning highlighted in the note that the border between Slovenia and Croatia at sea had not been determined yet and was subject to international arbitration.

This should be taken into account in the plans for exploration and exploitation of hydrocarbons, it said.

Additionally, the ministry highlighted that Croatian plans could have cross-border impacts, which is why neighbouring countries must be notified of Croatia's intentions.

While the UN protocol on strategic environmental assessment does not specify when a country should notify neighbouring countries of its intentions in such cases, it says this should be done "as soon as possible" but before any plans or programmes are endorsed.

The notification must contain a draft plan or programme, an environmental report, including information on probable cross-border impacts, and information on the decision-making process, including the deadlines for remarks.

If the affected party wishes so, consultations must be held on measures to prevent or mitigate any harmful consequences the project could have for the environment, while the public and the relevant institutions of the affected country must be regularly informed on the developments.

Six companies applied last year to Croatia's public call for exploration and exploitation of hydrocarbons in the Croatian part of the Adriatic Sea.

Contracts with the best bidders are to be signed at the end of the first quarter of this year. These will then start exploration, which should take three to six years.

The exploration zones are between 1,000 and 1,600 sq. kilometres in area. Eight are in the northern and 21 in the central and southern Croatian Adriatic Sea.