BRUSSELS (AFP) -- The European Union will warn Serbia today that talks on closer ties are in jeopardy over Belgrade's failure to cooperate fully with the UN war crimes court, as key suspects remain at large.

At talks in Brussels, EU foreign ministers will give added weight to a report by enlargement commissioner Olli Rehn which will lay out the former Yugoslav republic's shortcomings in meeting EU standards.

Hinting at the report's contents, Rehn warned last week that "we cannot avoid disruption of the negotiations" if Belgrade refuses to cooperate with the International Criminal Tribunal for former Yugoslavia (ICTY) in The Hague.

A decade after the war in Bosnia that claimed 200,000 lives and left more than two million homeless, the conflict's most wanted men, former Bosnian Serb leader Radovan Karadzic and military chief Ratko Mladic, are still on the run.

Both men have been indicted by the ICTY for crimes including ordering the Srebrenica massacre of 8,000 Muslims at the end of the 1992-1995 war. Serbian media reports on Tuesday and Wednesday suggested that Mladic, who is believed to have been hiding in Serbia, had either been located, was negotiating his surrender or was already under arrest. Belgrade denied this.

While Europe failed completely to prevent the Bosnian war, the prospect of joining the rich 25-member club has now become a powerful incentive for a Serbia ravaged economically by the conflicts in the volatile Balkans.

In November, Brussels and Belgrade began talks on a Stabilization and Association Agreement (SAA), seen as a first step toward EU membership, but Rehn's report will say that Serbia has fallen short of expectations.

"Cooperation (has) unfortunately deteriorated," he told European parliamentarians. "The political will should be translated into concrete action," he said. "It is now in the hand of the Serbian leadership to choose a European future instead of a nationalist past."

An EU official said that the European Commission, the EU's executive, could decide to put the brakes on the talks, slowing them down -- without actually calling a halt -- until Belgrade's progress with the court speeds up.

"If there is no full cooperation anytime soon, these negotiations cannot just continue as if nothing had happened," the official said.

This could mean the cancellation of the next round of SAA talks on April 5.

In the past, the foreign ministers have urged Serbia, and also Bosnia, to step up cooperation but with Rehn's report in hand and the Mladic incident in mind, they may be ready to go further.

"I think we will have to do this now stronger, because the time is now right for this," said a senior official with the Austrian presidency of the EU, on condition of anonymity.

"We asked for the message to be tougher than first planned and that it mention as explicitly as possible the link between continuing the SAA talks and full cooperation with ICTY, which should lead to Mladic's arrest sooner or later," an EU diplomat said.

Full cooperation is generally understood to mean ensuring that key indictees -- in this case Mladic and Karadzic -- are delivered to The Hague tribunal.

Last year, the EU delayed the start of full membership talks with Croatia, another of the former Yugoslav republics, for not doing enough to help the court find a major suspect, General Ante Gotovina.