Del Ponte's assessment before the UN Security Council differs from one she made in April this year and on the basis of which the EC adopted a positive decision on Croatia's membership application, Rehn said after meeting Foreign Minister Miomir Zuzul.
"We encourage and urge the government to do its utmost by mid-December to remedy this state of affairs and ensure full cooperation with the tribunal," he added.
European leaders will meet in Brussels on 16 and 17 December at a summit which is expected to adopt a decision on a date for the start of accession talks with Croatia.
The European Commissioner, who is on his first official visit to Zagreb, said that full cooperation with the Hague tribunal was a necessary condition for progress on the road to the EU. There are no short-cuts on the road to the EU, there is only one, regular way, which envisages full rule of law in all aspects, Rehn said.
The arrest of runaway general Ante Gotovina is the remaining stumbling block for Croatia and the EC and its member-countries insist on the full cooperation of the Croatian government and all administrative structures with the Hague tribunal, which will be the main criterion in establishing if there is full rule of law, he said.
As soon as this remaining obligation is fulfilled, our relations will have a bright future, Rehn said.
Minister Zuzul said that the Croatian government was determined to continue fully cooperating with the Hague tribunal "as there is no other model of cooperation, but one of full cooperation. I believe that in the future too we will be able to demonstrate that we are acting exactly that way".
Rehn welcomed Prime Minister Ivo Sanader's recent visit to Belgrade as an encouraging sign on the road of reconciliation.
Rehn is also expected to meet President Stjepan Mesic, PM Ivo Sanader, Parliament Speaker Vladimir Seks and European Integration Minister Kolinda Grabar Kitarovic.