Croatia says Italy's annual catch is ten times higher than its own

The protected area which covers 57,000 sq km (22,800 sq miles) is due to come into force on Tuesday.

Croatia says fishing stocks in the Adriatic are being depleted by Italy's fishing fleet.

But the European Commission has indicated that refusing access to member states could affect Croatia's plans to join the EU.

'Negative consequences'

The European Enlargement Commissioner, Olli Rehn, said Croatia's negotiations with the EU should enter a decisive phase in 2008 - provided the fishing issue was successfully resolved.

A unilateral declaration (of the zone), and particularly its enforcement, would greatly intrude on the sovereignty of the Republic of Slovenia Slovenian government statement

"It is essential that a solution is found... in order to avoid negative consequences for the country's EU accession process," he said.

Neighbouring Slovenia, which takes over the EU presidency on 1 January, has strongly criticised the planned zone.

A statement on the foreign ministry website said that Slovenia had supported Croatia's efforts to join the EU and as a result was "entitled to expect Croatia to act in a credible manner in this case".

Referring to unresolved sea borders between the two countries, it said the "unilateral declaration (of the zone), and particularly its enforcement, would greatly intrude on the sovereignty of the Republic of Slovenia".

Croatian cost

Croatia argues that Italian fishing deprives it of 300m euros (�219m) each year.

It complains that Italy's annual catch of 200,000 tonnes is ten times the size of its own.

But diplomats have been unable to make progress on the issue because of slow progress towards forming a Croatian government since elections there in November.

The prime minister-designate, Ivo Sanader, is not expected to form a cabinet until mid-January and his main coalition partner is strongly in favour of the protection zone.