(LJUBLJANA) - The European Union presidency warned Friday that Croatia's implementation of a protected Adriatic fishing zone violated EU rules and could jeopardise Zagreb's aspirations to join the 27-nation bloc.

"It is the custom in Europe to comply with all agreements reached, and if you don't like the agreement, you seek consensus to change it," Prime Minister Janez Jansa whose country holds the rotating presidency told a news conference.

"You can't just revoke such an agreement unilaterally," Jansa said.

With effect from January 1 -- the date also when Slovenia took over the EU presidency -- the Croatian parliament proclaimed the protected fishing and ecological zone covering an area of some 57,000 square kilometres (22,800 square miles).

Its goal is to protect Adriatic Sea fishing stocks which Croatia says are being depleted by Italy's larger fishing fleet.

Striving for EU candidacy in 2004, Croatia had agreed to allow exemptions for EU countries -- notably its neighbors Italy and Slovenia -- until a fishing accord was finalised with Brussels.

But Croatian Prime Minister-designate Ivo Sanader has yet to discuss the issue with his main coalition partner, the Peasants Party, which strongly advocates the enforcement of the zone.

The EU expects Zagreb to "solve this problem as soon as the new parliament constitutes and the new government is sworn in," Jansa said.

Already last month, EU Enlargement Commissioner Olli Rehn warned Croatia that by refusing to open up the fisheries and ecological zone to all other 26 member states would lead to "negative" consequences for Zagreb's EU accession negotations.

"Croatia voluntarily decided to start accession negotiations and to meet the conditions" for EU accession. "It currently is not fulfilling them," said Jansa.

He insisted that Slovenia would not use its position as EU president as extra leverage in the resolution of "pending bilateral issues with Croatia."

At the same time, his government would not allow the fact that it was EU president "to deter us from defending our legitimate interests," he added.

Ever since Slovenia and Croatia declared independence from the former Yugoslavia in 1991 they have been unable to resolve a number of bilateral issues, including their common sea-border, an issue linked to the Croatian Adriatic fishing zone.

Italy and Slovenia have themselves proclaimed ecological zones.

Croatia hopes to join the EU by 2010.

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