The European Union is set to delay membership talks with Croatia this week despite a last-ditch bid by Zagreb to show it is doing all it can to find a key war crimes suspect, diplomats said Tuesday.

The assessment came in spite of a last-minute unannounced visit to Brussels by Croatian Premier Ivo Sanader ahead of a meeting of EU foreign ministers Wednesday, due to discuss whether to let Croatia start talks on Thursday.

Most of the EU's 25 member states appear still to oppose giving a go-ahead for the talks until retired general Ante Gotovina is handed over to the International Criminal Tribunal for the former Yugoslavia (ICTY) in the Hague.

"It is very likely to be a negative decision," said one source, while another said the EU's Luxembourg presidency had indicated that the EU ministers "will conclude that the negotiations cannot a priori begin."

Gotovina, a 48-year-old retired general, is considered a war hero by many Croatians but is wanted by the UN war crimes court for the alleged murder of at least 150 ethnic Serbs during the final stages of Croatia's 1991-95 war.

He is also accused of plundering Serbs' property during the war, during which Serb rebels opposed Croatia's breakaway from the former Yugoslavia.

Reflecting the strength of Croatia's desire to start EU talks, the ex-Yugoslav country's prime minister arrived in Brussels unannounced Tuesday on the eve of the ministerial talks.

Diplomats quoted him as having underlined the scale of the efforts Zagreb has made to help UN war crimes prosecutors find Gotovina -- including freezing his assets this week.

"From our point of view we have done everything in our power," he said, quoted by a Croatian source.

Croatia, hoping to be the second former Yugoslav republic -- Slovenia became the first last May -- to join the European Union as early as 2007, was told in December that it could in theory start talks with Brussels on March 17 -- this Thursday.

But that green light was conditional on providing "full cooperation" with ICTY chief prosecutor Carla del Ponte -- who reiterated Tuesday that this was not the case.

On Wednesday EU ministers will agree a framework setting out the main subject areas to be discussed in talks on Zagreb's EU bid. Croatia has voiced hopes of joining the EU in 2007, but this target seems increasingly untenable.

"The presidency does think it possible to start the talks on March 17," said another diplomat, adding that it would be an "enormous suprise" if the decision was anything other than a delay.

On Monday Luxembourg Prime Minister Jean-Claude Juncker issued an ultimatum to Croatia, warning that Zagreb could only begin membership talks this week if it transfers Gotovina to the Hague.

"The negotiations will begin on March 17 provided General Gotovina is transferred, and this must be done," he said in a statement.

Juncker made his comments following a decision by Zagreb -- which insists it has no idea where Gotovina is -- to freeze the retired general's assets in a new attempt to help the ICTY find him.

The EU earlier hailed the Croatian decision as "an important step," but said Zagreb must still do more if it wants to start accession talks.

"There are other aspects and Zagreb's cooperation with the ICTY must be full," said an EU source, referring to the need for Gotovina to be handed to the court.